Sync with WebODF e50bc588ff3e380178ffabecfe2fbca92bef6aed

This sync introduces numerous features, performance improvements, and bugfixes.

### Notable new things:
* Keyboard support in iOS and other touchscreens.
* Pinch-zoom support on touch devices.
* SVG selections that look like those in LibreOffice.
* Major speed improvements with all editing operations and cursor movements.
* IME support on desktop browsers.
* Word-by-word navigation with Ctrl+Left/Right.
* Fixes for IE11.

Fixes #94, #148, #151, #208, #43, #174, #77.
Obsoletes #210.