allow different default directories for different operating systems

git-svn-id: svn://svn.icculus.org/fs2open@10499 387891d4-d844-0410-90c0-e4c51a9137d3
and for proper resolution of canonical directory paths in all cases, do things this way

git-svn-id: svn://svn.icculus.org/fs2open@10500 387891d4-d844-0410-90c0-e4c51a9137d3
remove some unused widgets

git-svn-id: svn://svn.icculus.org/fs2open@10501 387891d4-d844-0410-90c0-e4c51a9137d3
add more default directories

git-svn-id: svn://svn.icculus.org/fs2open@10502 387891d4-d844-0410-90c0-e4c51a9137d3
more aliases are nice

git-svn-id: svn://svn.icculus.org/fs2open@10503 387891d4-d844-0410-90c0-e4c51a9137d3
add localization!  (currently only English)

git-svn-id: svn://svn.icculus.org/fs2open@10504 387891d4-d844-0410-90c0-e4c51a9137d3
tweak, per niffiwan

git-svn-id: svn://svn.icculus.org/fs2open@10505 387891d4-d844-0410-90c0-e4c51a9137d3
add briefing icons for ship-with-cargo and wing-with-cargo

git-svn-id: svn://svn.icculus.org/fs2open@10506 387891d4-d844-0410-90c0-e4c51a9137d3