Cleans up side by side layout manipulation

The preview in side by side view is now located closer to the actual
editor textarea in the DOM, this requires less DOM traversal using
jQuery
Editor can only resize vertically in side by side mode

When in side by side mode the editor and the preview should both take
approximately 50% of the available horizontal space. Some browsers allow
textarea elements to be resized, which for this to properly work should
be restricted to only allow vertical resizes
Resizing the editor area resizes the preview

On some browsers it is possible to resize the editor textarea. Such
changes should be reflected in the preview window.

This behavior is now implemented by listening to and acting on the
mouseup event on the textarea. The current implementation is a
workaround workaround since the resize event does not work on individual
HTML elements
The wiki editing mode is indicated by a class on the html element

This allows for easier combination of different modes
Adds 'Writing Mode'

Writing mode removes all distracting elements from the layout of the
wiki edit page for full focus on the editor and the preview elements
Version bump to 0.2.0

Updates history with applied changes