Swap 'title' and 'releaseTitle' meaning

- Trasparent change: now it makes more sense.
- Updated tests to reflect 'title', 'releaseTitle' meaning swap.
- Improved documentation.

Signed-off-by: JoeLametta <JoeLametta@users.noreply.github.com>

whipper/command/mblookup.py

@@ -26,7 +26,7 @@ Example Disc ID: KnpGsLhvH.lPrNc1PBL21lb9Bg4-"""
         :type md: `DiscMetadata`
         """
         print('    Artist: %s' % md.artist.encode('utf-8'))
-        print('    Title:  %s' % md.title.encode('utf-8'))
+        print('    Title:  %s' % md.releaseTitle.encode('utf-8'))
         print('    Type:   %s' % str(md.releaseType).encode('utf-8'))
         print('    URL:    %s' % md.url)
         print('    Tracks: %d' % len(md.tracks))