Selected inline-styles were externalized to xterm.css.
The `Terminal._charSizeStyleElement` is removed since it
was not used anymore.
Fixes: https://github.com/xtermjs/xterm.js/issues/1335
Two parts were commented out:
- _writeStopped: This is because _xoffSentToCatchUp references this variable
and the feature is sort of half implemented/disabled.
- _clearChar: This is because some comments still reference this, it's part
of the work needed to do better line redrawing.
Fixes#1081
* Make sure character dimensions are available right after calling term.open()
* Do not assume var assignments are global anymore, webpack will isolate them
* Use DocumentFragment to build Viewport and helpers before attaching them to the DOM
* Shield term.focus call from crashing when used before term.open