Improve window sizing when toggling file browser

The first time the browser is toggled, we’ll save the current frame so that we can restore it if the user toggles again (the calculated frame won’t match when window is moved or width is “truncated”).

Additionally when file browser is on the left side, we reframe the window so that the text view remains in the same place on the screen.

Closes #827.
Clear previous frame when switching side of file browser
Add UI setting for disabling auto-resize

The auto-resize is when toggling the file browser.