small fixes to path functions
simple_http: change callback arguments and small fixes
gnome_mmkeys: add support for MATE desktop
fix occasional loss of cover picture for album with compilation flag
small improvements to the Progress function
add support for reading pdf pages as images

uses pdftocairo and pdfinfo command-line commands
mostly for use in PictureBrowser
simple_http: add support for filename suggestion from Content-Disposition

will be used by GMB::DropURI
lots of common code added to the 3 files, will need to reorganize that
add GMB::DropURI to handle copying/moving/downloading dropped files or url

meant to be used in PictureBrowser, but will probably be useful elsewhere later
add a few tiny utility functions
add new_scrolledwindow convenience function and use it
add support for passing options to widgets when opening a layout
add function to rename a picture
fix error when trying to scan album replaygain info
small improvements to BuildMenu function