don't use deprecated GtkArrow
Fix format not a string literal and no format arguments [-Werror=format-security]
Check NULL string when manipulate lists.
For example, fix that remove library and drop database, when eject any usb mass storage!.
* For these kinds of things I say that the device plugin are beta!!!! haha..
* (But the bug was not on the plugin!) haha..
Devices plugin: Properly handles devices that are mounted by the desktop before than by Pragha.
Show a message when fails to mount a usb..
Devices plugin: Stop using gtk_dialog_run.
Removable plugin: Ask as soon as the volume is detected, and do nothing until user decide to add the device.
MTP plugin: Remove unused and duplicate code.
Check existence of the files before import any playlist.
So.. never more import empty playlists!.
Trying to follow GLib/GTK+ best practices for the order of includes

Refactored includes to follow the glib best practices:
 * config.h (if required) * own module header file
 * system header files
 * required headers from current project

Inspoired on https://bugzilla.gnome.org/show_bug.cgi?id=735887
Equalizer dialog not need PraghaApplication.
The filter dialog either need PraghaApplication.
Remove useless option to setting gstreamer version.

Was readded by mistake on commit d54ce8c8
PraghaPreferencesDialog not depend on PraghaApplication.

Some changes are automatic, and others depend on accept or cancel the dialog. That it is better?
Merge branch 'master' into wip-header-bar

Conflicts:
	src/pragha-toolbar.h