General purpose replay

Complementing visionx::record, this MR introduces the VisionX core functionality of replaying any image sequences (chunked image sequences, legacy or primitive image sequences, video files) in visionx::playback.

This MR also introduces a new component utilising the new core functionality, the PlaybackImageProvider, which is able to replay single or multi-channel recordings with the aim of eventually deprecating the ImageSequenceImageProvider or the VideoFileImageProvider. It was designed to minimise configuration efforts and does therefore not offer as much configuration options as the other two.

• To playback a video file, for example /path/to/vid.avi, it is enough to set the recording_files property to /path/to/vid.avi.

• If you want to playback a stereo image sequence recording, for example /path/to/vid/frame_right_*.jpg and /path/to/vid/frame_left_*.jpg, you can set recording_files to /path/to/vid/frame_right_*.jpg;/path/to/vid/frame_left_*.jpg, or /path/to/vid/frame_right*jpg;/path/to/vid/frame_left*jpg, or /path/to/vid/frame_right_*;/path/to/vid/frame_left_*, or anything else uniquely identifying the frames of the left and right camera. The ";" character is used to separate the channels.

• If the frames are split into distinct directories, like: /path/to/vid/right/frame_*.jpg and /path/to/vid/left/frame_*.jpg: Set recording_files to /path/to/vid/right/frame_*.jpg;/path/to/vid/left/frame_*.jpg. You can also set the base_path property, so that the paths in recording_files will be interpreted relative to that path: base_path=/path/to/vid/ and recording_files=left;right

• The number of channels is not limited - paths are separated by ";" => recording_files=source1;source2;source3;...;source_n.

• The order of recording_files is considered, so changing recording_files=source1;source2 to source2;source1 will swap the channels.

• Other options are: loop (set to true to loop the playback, false otherwise), fps_lock (lock the FPS to that amount, ignoring what was derived from metadata or guessed), fps_multiplier (speed up (value > 1) or slow down (value < 1) the recording)

Please note: The ImageMonitor GUI plugin is not designed with changing amounts of image sources in mind, and I also do not think it is worth the effort to make it aware of that (I cannot even think of a use case). This just means that if you have an ImageMonitor connected, and you change the number of channels, the ImageMonitor may segfault.

Other changes:

• Use boost::filesystem instead of POSIX (boost::filesystem is API-compatible to C++17 std::filesystem (and C++14 std::experimental::filesystem) (this implies breaking API changes in visionx::record, even though they are trivially resolved and no one depends on it yet anyway)
• Add default constructors for visionx::record strategies
• Remove padding from chunked image sequences for recording (no reason to do so, and it just restricts the recording because the number of frames is not known in advance)