MythMusic: look for icons in the MusicArt storage group
MythMusic: move metadata and tag reading/writing to libmythmetadata

This allows both MythMusic and mythbackend/mythutils etc to use the same code.

NOTE: a distclean and re-run of configure in both core and plugins is required.
Also this makes TagLib a mandatory dependency of core MythTV.
configure: try to fix the failing taglib checks
configure: try to fix the failing taglib checks (part2)
configure: try to fix the failing taglib checks (part3)
Remove a menu item that crept in as part of [df0cdfe8]
MythUIWebBrowser: when changing the zoom level display it on the status bar
MythMusic: Fix compilation on Darwin after [d6b0ae43]

Signed-off-by: Paul Harrison <pharrison@mythtv.org>
MythUIWebBrowser: make the zoom level a live setting

This makes the web browser save the zoom setting when changed and will use the
same zoom level when reopened.

Make the default zoom if not set 100% since most web pages look best at that
zoom level.
MythUIWebBrowser: set some sensible bounds to the zoom level 0.3 to 5.0
MythUIWebBrowser: correct a comment