Cairo-Dock Core 3.1.2

* **Core**: [by Fabrice Rey & Matthieu Baerts]
 * Dialogues Mgr:
  * cairo_dock_set_dialog_message (used by Help): used markup if it's needed
  * Fixed 2 bugs when an icon holding a modal dialog is destroyed
 * GUI:
  * Search for an icon path if the module gives us only the name of its icon (e.g. Deluge, Transmission, Menus)
  * Simple: Behavior: Position of the taskbar: 'After a given icon' choise was missing
 * Icon Mgr: removed a now useless static mutex
 * Init:
  * Initialised threads on new versions of GLib (>= 2.24)
  * This should finally fix a crash when opening Logout menu
 * Help: Used markup for the dialogues
 * Menu: Quit with a Cairo-Dock session: check if it's really the shift key which is used to unlock the quit menu entry

* **Plug-ins**: [by Fabrice Rey & Matthieu Baerts]
 * Clock: If seconds are not shown, redrawn the applet each time at 00 second (before the timer wasn't started with a delay and the applet was redrawn between 00 and 60 seconds)
 * GMenu: Editor: also check if 'menulibre' is available
 * RSSreader:
  * Make the text selectable in the dialog
  * Fixed incorrect duration of the dialog when no URL/connection
 * MusicPlayer: if the music player has given a wrong .desktop filename, check if it's a valid name before doing something more
 * Status-Notifier:
  * When the icon theme changes, remove the previous one first
  * Position of the Menu: e.g. with Dropbox: the menu is out of the screen every time something has changed in this menu (it displays 'connecting', free space available, etc.) -> we need to reposition it.
  * Fixed lots of corner cases (mainly for Skype)
  * Added full support of the Ubuntu indicator application API, for program that only use this one (and not the standard Status-Notifier API), like Skype
  * Implemented an horrible hack for Skype (it only creates its item when the host appears, not if the host already exists)
  * Updated the property HasStatusNotifierHostRegistered to IsStatusNotifierHostRegistered
  * Check for item unicity on creation (fixes the Skype double item)
  * E.g. with Dropbox, the menu is firstly drawn out of the screen and then it's ok
 * Misc.:
  * CMakeLists.txt: DBusMenu GLib and GTK are needed for Indicator-Applet

* **Third-Party applets**: [by Fabrice Rey & Matthieu Baerts]
 * GTG:
  * Supported both old (0.2) and new (0.3) versions
  * Handle the case where we receive the child before its parent
  * Used the GTG icons from the icon theme if available
  * Tried to reconnect to GTG when building the menu if it's not connected (if GTG is installed after or has been launched with a delay at startup
 * MintMenu: updated to match the latest version of MintMenu (that uses mateapplet instead of gnomeapplet)