robot state memory update

Disclaimer: sorry, a bit messy; more changes than initially expected due to changes in base class: MemoryConnector.h (now using a PluginUser class) has been removed. The PR https://gitlab.com/ArmarX/RobotAPI/-/merge_requests/141 should be merged first as I started from there.

Changes to RobotStateMemory:

• The robot state memory now has 3 segments: Localization, Proprioception and Description. The latter stores the robot description, so to say the "information to instantiate a robot model". Currently, I only store a XML file link there, but in the future, it should be the robot nodes and its properties to track changes over time (e.g. installing a new camera, changing hands, ...)
• The robot state memory core segments are now implemented in separate files, each is called Segment.h, similar to the object memory. This segment class has an attached visu class to allow memory-side visualization (to ArViz). Visualization can be turned on and off via properties.
• as the robot state memory and the object memory (the articulated objects in particular) use the same XML Aron definitions, e.g. Robot, RobotDescription and RobotState, there is a new library armem_robot to avoid dependencies between armem_robot_state and armem_objects.

Further changes:

• All my memory client classes, e.g. TransformReader are now refactored: As mentioned, the MemoryConnector class is now gone and replaced by memory Client**ComponentPluginUser classes.

source/RobotAPI/interface/armem/query.ice

@@ -49,6 +49,57 @@ module armarx
                         long first = 0;  ///< First index to get.
                         long last = -1;  ///< Last index to get (inclusive).
                     };
+
+
+                    /**
+                     * @brief Get snapshot(s) around timestamp.
+                     *
+                     * If there is a snapshot which exactly matches the query timestamp,
+                     * the behavior is as for the @see Single query. 
+                     * 
+                     * However, if there is no matching timestamp, the snapshots before 
+                     * and after the query timestamp will be returned.
+                     * 
+                     * If #eps is positive, the snapshots must be within the time
+                     * range [timestamp - eps, timestamp + eps]. 
+                     * Consequently, the query result can be empty.
+                     *
+                     * Hint: 
+                     *   This query can be quite useful when interpolating snapshots
+                     *   is possible.
+                     */
+                    class TimeApprox extends EntityQuery
+                    {
+                        long timestamp = -1;
+                        long eps = -1;
+                    };
+
+                    /**
+                     * @brief Get the last snapshot before or at the timestamp.
+                     * 
+                     * This query is kind of similar to latest() but with a reference timestamp.
+                     * 
+                     */
+                    class BeforeOrAtTime extends EntityQuery
+                    {
+                        long timestamp;
+                    }
+
+                    /**
+                     * @brief Get the last snapshot before the timestamp or a sequence of 
+                     *           n last elements before the timestamp depending on #maxEntries
+                     * 
+                     * Depending on #maxEntries, the behavior is as follows:
+                     *  - #maxEntries == 1 => last element before timestamp
+                     *  - #maxEntries > 1  => n last elements before timestamp
+                     *  - #maxEntries < 0  => all elements before timestamp
+                     */
+                    class BeforeTime extends EntityQuery
+                    {
+                        long timestamp;
+                        long maxEntries = 1;
+                    }
+
                 }