remove m_random_gp
fix #1395
Merge branch 'm_random_gp' of https://github.com/konstin/stk-code into konstin-m_random_gp
Try to convert m_gp from a GPData pointer to a GP object, compiles, but
crashes.
Merge branch 'master' into konstin-m_random_gp

Conflicts:
	src/states_screens/dialogs/gp_info_dialog.cpp
Mostly cosmetic changes (renamed variables, added comments). Changed
'random' constructor of GrandPrixData into a function so that there
is no need to create a new GPData objects and then copy it.
Merge remote-tracking branch 'origin/master' into konstin-m_random_gp
Merge branch 'konstin-m_random_gp'