#24 Support for embedded covers

[Tanyel A. Nimeu]

This patch uses id3libs' capabilities to add support for embedded covers.
A new file chooser input is added to the main window, so the user can select an image file to be embedded directly into mp3 files.
libmagic is used to determine the mimetype of the selected file. Currently only image/jpeg and image/png are accepted.

Based on ripperX 2.7.3
This patch depends on 01-revise-parse_rx_format_string.patch (see patch ID 3167133)
and should be applied with 02-playlist-name-config.patch (see patch ID 3167134)
and 03-albumartist-format-variable.patch (see patch ID 3167138)

[Tanyel A. Nimeu]

Support for embedded covers