Mantis #3004: standardize checks for whether ships can depart to docking bays, and whether departure goals are achievable, and whether a ship can be commanded to depart; also fix the default behavior if a ship attempts to warp out but is unable to

git-svn-id: svn://svn.icculus.org/fs2open@10428 387891d4-d844-0410-90c0-e4c51a9137d3
Mantis #3004: don't remove subspace drives from support ships

git-svn-id: svn://svn.icculus.org/fs2open@10429 387891d4-d844-0410-90c0-e4c51a9137d3