Make collision environment available to kinematics solver

[timonegk]

Is your feature request related to a problem? Please describe.
Currently, it is not possible in MoveIt to have collision-aware inverse kinematics, i.e., inverse kinematics solvers that include environment objects in their solution.

Describe the solution you'd like
It would be nice if the CollisionEnv or PlanningScene objects could be made available to the kinematics solver, for example by adding a parameter to searchPositionIK or passing a pointer to the object on initialization of the plugin.

Describe alternatives you've considered
The current rejection-based approach (providing a callback for collision checking that is executed after a solution has been found) is not sufficient for scenarios with more collisions and limits the options for kinematics solvers in this regard.