Fixed the undo bundo border
Start of the work on layout selector
Some layouts
Implementation of a layout selection tool.
Hid the slide layout selection widget created by the Xtige template
Layout modifications can now be reversed using the undo tool
Changed the design
Fixed the sporadic faulty behavior of the toggle menus
Implemented a third slide focus detection algorithm that should cope with all issues provoked by slides with small heights
Fixed css
Drag and drop with slide previews now moves the corresponding slides.
Refined the interaction for drag&drop. Droping on a preview now swaps the two contents.