* add DynamicsWorld::{getObjects, removeFloorPlane, clear)
* add DynamicsEngine::removeFloorPlane
* add BulletEngine::removeFloorPlane

* modernize-shrink-to-fit
* modernize-use-nullptr
* modernize-use-equals-default
* modernize-use-equals-delete
* modernize-unary-static-assert
* modernize-use-bool-literals
* modernize-replace-random-shuffle

    modernize-avoid-bind
    modernize-deprecated-headers
    modernize-redundant-void-arg
    modernize-replace-auto-ptr

* all camke module files are now in simox/CMakeModules
* FindBullet also uses Bullet_DIR to detect bullet
* Simox checks whether Bullet uses single or double precision
* removed the option SimDynamics_USE_BULLET_DOUBLE_PRECISION
* Set default for Simox_BUILD_SimDynamics to true (a warning will be printed if bullet is not found and SimDynmics will not be build)

Some were already using it and this should be uniform to work properly.

the friction coeffitient of the floor plane can be modified; more meaningful error messages for Hierachical IK

it now:
* uses layouts
* can reload a robot
* can deactivate robot self collisions
* shows more information about the simulation

The 6DOF joint implementation was not functional and not in use.