[Review Only] Randy/splitview pane header

Replace pane border highlighting with header.

TODO:
- [x] Fix editor sizing so horizontal scroll bars are not truncated from bottom
- [x] Fix empty editor to show logo
- [ ] Italicize header text

@JeffryBooher 
man my spelling is bad.  I can't figure out if it's my spelling or my typing skills that have gotten worse over time. Definitely my eyes have :)