Replaced tinymce 4 files with tinymce 5
Moved from unsupported 'light' skin to new 'oxide' skin included with v5.0
Default theme has been changed from 'modern' to 'silver'
Changes to tooltoggle plugin to work with new version
Updated behat steps for change in class names
Styling changes

behatnotneeded

Change-Id: I731962f8c522358034178528846aa0c35187d74a