Requests for future UI improvements

These are some of the remaining UI updates that are desirable:

- [ ] Update dropdown icons (we need some nicer ones)
- [ ] In tablet/mobile mode, put filename and MEI status into the top navbar instead of the pancake menu
- [ ] Add option to edit filename
- [ ] Improve Edit panel: The various edit buttons and options are a little ad-hoc and could use some improvement. Perhaps adding more titles to the various button sections?
- [ ] Replace PNG icons in the Insert panel with SVG icons.
- [ ] Finish getting rid of Bulma - it's an unnecessary dependency we use for CSS styles. I got rid of a lot of it already, but there are a few places where we still use it.
- [ ] Automatically close dropdowns when a user clicks on any of the items inside them.
- [ ] Make loading animation appear properly (seems to not work), and move it inside the editor (where image and SVG are displayed).
- [ ] Make the icons in the top navbar change colors on hover (just like the text). This will probably require the creation of a separate set of icons in different colors unless we want to use inline SVGs (which can get messy quickly) to update the colors dynamically.