Make sure gutter is redrawn when a document is shifted

Issue #2498
[compression helper] Use CodeMirror for code field

Dog food, and all that.
[runmode addon] Pass state to blankLine

Issue #2502
[foldcode addon] preventDefault clicks on widgets

So that the click doesn't kill editor focus.

Closes #2505
fix transpose char to work at start and end of line
Merge branch 'master' of https://github.com/marijnh/CodeMirror