Various improvements to Half-Life 2 map scripts.

[knoxed]

Work in progress!

Fixes to default HL2 map scripts.

• Fixed spawnflags on all point_viewcontrol entities in d1_trainstation_01. You could move inside the intro after some time elapsed.
• Refactored all possible checkpoints to use the new format. Checkpoints with additional outputs and conditions are left as is for now.
• Issue d1_canals_01 Various issue #339 has been taken care of.
• Improved some checkpoint positions and corrected loadout additions.
• Fixed d2_coast_07 is reloaded from scratch after d2_coast_08, except combine_gunship (if it is not destroyed) #363 and coast_07 gate doesn't open #364 hopefully.

Notes on certain maps

canals_08

• Removed 2nd checkpoint since if you'd die and respawn it would be even further away from the dock and airboat.
  Or, keep that one but also add another one somewhere (where?)

town_02

• This map is used two times therefore has checkpoints with special conditions (might not be possible with new format)

[knoxed]

This should be it for this PR, it's already quite big. I think everything is as it was except some position fixes but that's about it.