This is reverting templates back to pre-3.0 conventions,
which were dominated by XHTML templates.
HTML5 allows both self-closing and unclosed tags,
so opting for self-closing to achieve maximum compatibility.
HTML in tree nodes is already used to render page icons via SiteTree->TreeTitle.
In order to select the initial value correctly via HTML5 data attributes,
we need to encode any HTML values.
* Use jquery ui accordion for the field, and implemented an admin theme.
* Made the setting of configuration consistent with other form fields.
* ToggleComposteField->startClosed() has been deprecated in favour of
setStartClosed().
* Removed public access to the heading level, instead use getHeadingLevel()
or setHeadingLevel().
1. Modified gridfield to use default colours
2. Added ability to show and hide the filter
3. Design changes to icons used
4. Gridfield template fixes: Took out broken mark-up from templates
(spans were being inserted inside spans), and adjusted styles. Added
extra class to template
5. Added "filter by ..." placeholder text to input fields
BUGFIX Remove legacy code and template which is never picked-up so that TextareaField becomes 'readonly' when it is transfered to readonly field. Change TextareaFieldTest test cases to address a 'readonly' textarea field displaying the special html characters correctly.
