Memory editor

[parasyte]

The goal of this PR is to turn the memory viewer into a fully functional memory editor.

• [ ] Add edit cursor and commit with Enter.
• [x] Add selection ranges.
• [x] Copy as text.
• [ ] Copy as binary.
• [ ] Paste text or binary.
• [ ] Basic navigation.
  • [ ] Follow pointer with ctrl+click.
  • [ ] Follow stack; Go back with ctrl+-.
  • [x] Bookmarks.
• [x] Session storage.

The design for the editor will keep a buffer of user input that is shown in a different color until the buffer is committed with the Enter key. This will allow the edits to be applied atomically while a game is running.

[parasyte]

This isn't done yet, but I'm going to merge it because it's stable and I want to use the new session stuff in here for other things.