Move hard-coded rstation processing logic for stellar file to init.nut

The Resource Station is one of a few classes that can be defined in the
stellar structure definition files.  The logic is hard-coded into
CoordSys::readFile(), but it's best implemented in a script for easy
customization.

The hard-coded logic is commented out anyway.
Separated RStation-draw.cpp from RStation.cpp

Also added Doxygen comments on top of each files.
Make RStation be rendered visible

The class have not had a model to show, because it has been stuck with
precompiled .bin files which are obsolete.
Add a initialization script for RStation

The added script is RStation.nut.

Overlay icon fo RStation objects are added, too.
Add maxRU and defaultRU variables to RStation's initialization scirpt
Add modelFile parameter to RStation's initialization script
Delete obsolete and commented out codes from RStation
Add maxOccupyTime variable to RStation initialization script

The alphacen.nut mission demonstrates it.