Create a separate scenemanager for each CharacterPreview instance
include members of BSAArchives in Ogres resource indices
reworked DirArchive to improve performance

Replaced old file index with a simple map. The map works by storing the
file's relative path with path seperators normalized, and in lower case if
not in strict mode. Incoming searches are normalized in the same way then
the name is searched in the map. The value in the map is the original full
path to the file which is then used to created a ConstrainedDataStream. In
addition to changing the index, the commonly used Archive methods are
implemented so that they don't fall back on the default FileSystemArchive
implementations.
Merge remote-tracking branch 'blunted2night/issue_460'