Initial support for AIFF files with ID3 tags.
Added tests for True Audio to make sure the recent ID3 changes didn't break anything.
AIFF: Support also the .aifc file extension.

This is sometimes used for "compressed" AIFF (AIFF-C) files.
Travis-CI: Make sure mutagen 1.23 gets installed.

This is the new minimum version for supporting AIFF files.
Do not require mutagen 1.23 but disable AIFF support for older versions.
Merge pull request #376 from phw/aiff

PICARD-42: Support AIFF files