refactor and extend usability (v 3.0.0)

* add on/off button to toolbar
* add highlighting table, hr ----, sign ~~~
* update codemirror lib to 4.7
* fix font size

Change-Id: Idd5775d6c80a18406aee7b8ab51691f26038764c
Merge "refactor and extend usability (v 3.0.0)"