WIP Minimal client-side editor part of Stackedit

**WIP**: WORK IN PROGRESS, do not merge this branch

This branch removes all server-side parts, and special code for handling www.stackedit.io, google analytics, and more.

The goal is that this should provide a clean split-panel editor without extra bells and whistles.

* [ ] Remove server-side part
* [ ] Remove google analytics
* [ ] Remove all third-party integration points:
  - [ ] twitter
  - [ ] google drive
  - [ ] picasa
  - [ ] github
  - [ ] couchdb
  - [ ] dropbox
  - [ ] blogger
  - [ ] google+
  - [ ] tumblr
  - [ ] wordpress
* [ ] remove special edge-case syntax handling of markdown
  - [ ] remove mathjax
  - [ ] remove flowchart/uml
* [ ] Remove extra css stylesheets, there is only need for one stylesheet here
* [ ] Remove all settings and provide some decent defaults.