Added tab style to interface prefs panel.
Merge branch 'master' of https://github.com/sirjuddington/SLADE
Restored ability to use enter on offset input.

At least on the GfxEntryPanel. I think this will be heavily needed on
the texture editor too.
More Eternity things from Bifröst.
Eternity's Doom copies in 6000 range.
More options in map display prefs panel.

Thing angle arrow options, to be precise.
Double-clicking a texture def entry will focus it.

When double-clicking a PNAMES, TEXTURE1, TEXTURE2, or TEXTURES entry, or
clicking on the "Edit Textures" button from this entry's default panel,
the texture editor will open or be selected as usual, but will also
select the proper tab. (One cannot believe how long this has bugged me.)
Merge pull request #70 from Gaerzi/master

Sync with my fork.