Fix: Picard crashes if a plugin can not be loaded.

Signed-off-by: brainz34 <brainz34@musicbrainz.org>
Provide better activity stats in the status bar

Partial solution to PICARD-478
Remove un-needed num_saves method
Make track lengths within 1s of each other match

Due to minor timing differences when ripping a CD, it is common for
tracks to differ by up to 1s in length.

This commit enhances metadatabox to show lengths +/- 1s as matching.

Note: Means of converting mmm:ss to seconds is not elegant - anyone with
a better solution please say.
Changed to implement bitmap's alternative approach
Provide more consistent status bar info and code

Still need to make "Unmatched Files" and "Clusters" FileTreeItems
consistent.
Fix vertical alignment with right-aligned lengths
Merge pull request #111 from Sophist-UK/sophist_fix_qtreeitem_vertical_alignment

Fix vertical alignment with right-aligned lengths
Change matching fuzziness to 2s
Merge branch 'Sophist-UK-sophist_match_track_lengths_within_1s'
whitespace
Rename stuff to better reflect usage
Add cluster count
Address review comments
Merge branch 'sophist_improve_status_counters' of git://github.com/Sophist-UK/picard into Sophist-UK-sophist_improve_status_counters
Fix tests for cover art vs formats, they couldn't fail.
Reduce cover art vs formats test code redundancy.
Fix test_ape failure due to incorrect APEValue type (auto)detection.

Force APEValue type on save to mutagen.apev2.BINARY, it is needed because
mutagen is trying to detect type, and set it to TEXT, and when it is tested
on load (apev2.py _load()), it doesn't detect cover tag because it isn't of
the BINARY type as expected.
Fix test_mp4 failure AssertionError: 'image/jpeg' != 'image/png'

value is already a MP4Cover, calling it again just set the format to default
JPEG, causing this issue on load.
Merge branch 'tests_formats_fix' of https://github.com/zas/picard