Fix memory leaks in TextureXList

Release stored CTexture objects on destruction of TextureXList
Fix memory leaks in DoomJagSpriteDataFormat

Release uint16_t array before exiting DoomJagSpriteDataFormat::isThisFormat() function
Merge pull request #139 from alexey-lysiuk/fix_memory_leaks

Fix memory leaks
Merge branch 'master' of https://github.com/sirjuddington/SLADE into osx