Fix display of collection in overlay info.

Fix display of collection in overlay info.
Due to markup escaped <i>collection</i> was displayed instead of collection's in italic.

Overlay info syntax was extended to allow the wrapping of displayed data with markup.

General syntax is: %name[:length limit][:extra]%
Extra string uses special character '*' to mark the place of the data to display.
If no '*' is present, then extra string is just appended to data.
Any "\n" is replaced by a newline on display.
Pango mark up is accepted in left and right parts.
If data is empty, nothing will be displayed.

Examples:
"%name:<i>*</i>\n%" -> name is displayed in italics ended with a newline
"%size:\n%"         -> size is displayed with a newline at end
"%formatted.ISOSpeedRating:ISO *%"      -> prefix iso number with "ISO " (ie. "ISO 100")
"Collection <b>*</b>\n" -> display collection name in bold prefixed by "Collection " and a newline is appended

Collection name formatting was slighly improved by not displaying the .gqv extension.
The default overlay info string was modified to use the new syntax, but older info strings should be
displayed as usual.