cpplib: Add transposed vector accessor to Mat4

Although this version does not allow modification of the matrix via returned reference,
they are very handy.
Merge branch 'cpplib' into next2
Make use of new cpplib::Mat4::tvec3() in GLwindowSolarMap::drawMapCSOrbit
refactor: Erase ancient codes that will never be used even for reference
Add getter method for orbit center body of OrbitCS
Make OrbitCS::flags2 hidden inside the class and added accessors for it

OrbitCS::{get|set}ShowOrbit() provide access to the flag.
The flag is not necessarily a bit field since the implementation details
are hidden from the public.

Also enabled solar map to display orbit ring for binary system.
Merge branch 'next2' into gdnext
gundam: Adapt move of EntityRegister definition