Add intermediate points to make quick free drawings smoother.
Do not redisplay the area at this step (crashes).
Use device.get_coords rather than global.get_pointer because the later return rounded (floor) values.
Fix#45.
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.
* Import palettes from a .gpl file (one palette for each column).
* Add possibility to use more than 9 palettes.
* Color display names support.
* color.toJSON for svg and drawing saves, color.toString for display.
The color picker use the ["Color Picker" extensions](https://github.com/tuberry/color-picker) if it is available thanks to `pickAsync` "api". In comparaison to the GS color picker, it provides a colored cursor and a menu to adjust the color.
* element.x and element.y are relative to the area, not to the stage.
* Do not hide and do not set opacity to 0 because ibusCandidatePopup need a mapped text entry to init correctly its position.
* Rename "Persistent" to "Persistent over restarts".
* If disabled, "Persistent over toggles" has priority over "Persistent over restarts" and "Drawing on the desktop".
Close issue #42.
* Pass Clutter color and Pango fontDescription objects to elements, not strings.
* Do not use the color format '#rrggbbaa' in svg since it is not supported in GNOME 3.24.
* 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.
* It is no longer required to clamp the setting value in area.js.
* Add a "range" property, completed with another 'step' property, to PixelSpinButton in order to directly initiate the lower and upper values of the adjustment from the relevant setting range.
* Not related: fix an inversion between Pango and Cairo in element.js.
Since the most drawing params can be changed via menu or shortcuts, remove default.css and user.css.
* Missing params like palettes, dash, grid, etc, are added to prefs.
* Add palette choice to menu and shortcuts.
* Some defaults like fonts, line width, etc, are no longer modifiable by the user.
abakkk