reorganize editor menu

[johanneswilm]

Size: The editor's menu is problematic because it has an extra button for each thing that can be inserted. This means we cannot add more things without overloaidng big screens, and as it is, FW doesn't work well on small screens.

Usability: In order to modify a figure, one needs to select the figure, and then hit the figure button. This is not very intuitive.

Possible solution: Make just one drop down menu "Insert..." and put all the other items into it, thereby freeing up screenspace. Then only show the separate figure/citation/etc. button if a figure/citation/etc. is currently selected, and hitting the button will allow the user to change any of its attributes. The appearance of the button which isn't there normally should give a visual clue to the user that this may be what to press to make changes.