Radiation pressure models (extended)

[DominicDirkx]

This pull request supersedes #184, and includes the following extensions to the code there:

• Removal of old radiation pressure acceleration/interface models. User interfaces for cannonball radiation pressure models are retained, and are backwards compatible (but will use the new source/target/acceleration model)
• Adding of acceleration partials for the new framework. Analytical partials are used for a point source (with a panelled or cannonball target). Extended sources (albedo/IR) use numerical partials
• Splitting off of vehicle surface panelling into a new class structure inside VehicleSystems, to support moving solar arrays, antennas, etc., with their rotation w.r.t. the body frame defined by a dedicated rotation model, and the future extension of the same panels to other surface force calculation

Open points (which will be tracked through separate issues/pull requests, and do not need to delay the merger of this one)

• Python interface pull request
• API reference entries
• Website user guide update (based on: Radiation pressure models tudat-space#122)
• Deprecation notices to users when using old interface
• Unit tests of radiation pressure for moving vehicle parts
• Unit tests of time-variable source luminosity
• Unit tests for custom surface property distribution