New markdown editor. Close #2

Added markdown editor for Mojo-Twist blog engine. I know that commits must be small and often.
I could not found the corresponding code to create a small commits. Sorry.

CHANGES:

+  Added 2 routes in `Twist.pm`: for preview markdown and for save markdown
+* Added 3 new methods and modified method `preview` in `Editor.pm`:
  + `prerender` returning json object containing html markup for uploaded markdown
  + `save` creating files to new markdown
  + `_write` writing header and content to created files
  * `preview` additionally returning json object if request header containing type 'application/json'
+* Updated `style.css`:
  * changed shadows of images
  * fixed line height for gist pastes
  * changed icons
  + added styles for new editor
-  Removed all files of first implementation of editor
-  Removed include prettify.js script from template `editor-preview.html.ep`
*  Added class 'Editor' to `frame.js`
*  Updated custom font files: added icon for [cut]
*  `.gitignore` ignoring path '.sync' in root directory
AJAX: async requests
Added loader
Added AJAX error handler
Merge branch 'feature/new-editor' into develop
Bump version