Replace CanCan with CanCanCan
Use full asset url for tinymce base path, if asset host is set.

Closes #596
Complete new README

Added much more useful information into the readme that should help to get started with Alchemy even better. Closes #632
Set positions on elements manually while ordering

We do not use acts_as_list methods anymore which saves database quaries. This change also ensures the correct position of the elements.
Fixes "publish page" specs
Updates the tinymce skin, so the editor still looks good w/o toolbar
Merge branch 'master' of https://github.com/magiclabs/alchemy_cms
Merge branch 'master' into tweaks