Adding outline for editor

It is now possible to edit bytes, though the editor isn't very smart.
That comes next.
Adding editor down into the model

Now the runs have the option of implementing an editor. Currently no
editor is implemented correctly - but all the framework is there so I
can.
Refactor

Parser and MainWindow are getting too long.
Parser is easy - it is already broken into multiple classes. All classes
dealing with RunStorage have been moved to a new file.
MainWindow is a bit more complex. All the cursor logic (moving
left/right/up/down, highlighting, etc) has been moved to a helper class.
The new class accounts for 165 lines, but MainWindow is still a little
too long. Something else needs to be extracted.
Write the editor code

Now that all the plumbing is in place, I've completed the actual editors
for strings and default. Lz compressed data, pointers, and the header
are purposely not editable right now.