With old GS/GJS, some GType names were generated from class names without sanitizing it (e.g. Menu.ActionButton).
Instead of defining all GType names, sanitize all class name as it was GType name, and let GJS generated GType name securely when it is necessary.
Fix#46.
* A minimum width for the menu, the same as the aggregate menu, in order to prevent the menu with from growing on submenu open.
* A maximum width for uncontrolled content (font, image and drawing names). Same value and same reason.
* Style the font family labels in idle loop to open the submenu fastly.
* Add the drawing gicons in idle loop to open the submenu smoothly.
`directory.monitor(...)` -> `directory.monitor_directory(...)`.
It is important to specify that the file to monitor is a directory because maybe the directory does not exist yet and remove events would not be monitored.
* Let the user choose the directory.
* Rework of Files.Images.
* area.currentImage is now an ... image, not an index.
* Add 'switch-image-file-reverse' keybinding.
* Add image gicons (from thumbnails) in the submenu.
* Images are reset on drawing mode left or on images added from the clipboard.