Changes include:
* Much better encapsulation of textview/textbuffer, with each isolated
responsibility living independently on its own class/file.
* Less code overall
* Various small fixes around the components involved, such as:
  * Indentation of nested lists (fixes #120)
  * Unwanted scroll on select all (ctrl+a)
* Removal of unused code around the components involved
* Fixes for scrollbar location, now at the edge of the window