BUG: Adjust css for actions toolbar on pages (fixes 7649)

Set a minimum height on the actions panel so it would look the same in
list and tree views
BUG: IE7 vertical text fix

Re-add vertical text fix, as it's been overwritten somewhere along the
way
GridFieldSortableHeader now allows composite fields to be sorted based db fields (see #7601)
NEW Allow querying if a field exists on a table
BUG: Fix an issue caused by moving a page from one location in the tree to another location doesn't update parent id in the edit form immediately (see #7740)
The issue causes the moved page to revert to previous location when Save and Publish before any page refresh or page switching.
This commit also adds 'Modified' badge to the moved page
FIX #7787 Handles ajax and normal requests differently when validation fails on gridfields
NEW Custom menu icons for the CMS main menu

Add optional custom menu icons to the CMS main menu for every class
extending LeftAndMain (ModelAdmin). Works by setting optional static
$menu_icon = '/path/to/image' and providing custom styling for added
icons. Works for the menu as well as icon in the right-side (GridField) pane header.
BUG Allow custom getters in summaryFields() (fixes #7788)

Regression from ca1d38dffdb
Merge pull request #746 from phalkunz/7601-listview-sort-by-title

GridFieldSortableHeader now allows composite fields to be sorted based db fields (see #7601)
Merge branch '7740-re-ordering-page' of git://github.com/phalkunz/sapphire into phalkunz-7740-re-ordering-page
LeftAndMain::$session_namespace

More fine-grained control over session storage,
particularly when reusing the "current page" state.
Merge pull request #752 from silverstripe-big-o/session-namespace

LeftAndMain::$session_namespace (#7815)
FIX If ClassName read from DB doesnt exist, dont break

We know the subclass of a record by its ClassName value, but code changes
might have meant that class no longer exists. We used to just break,
but this patch overrides the apparent value of ClassName to be
one that exists in that situation
DOC Gave easier instructions for would-be authors

The use of GitHub for documentation isn't ideal in a world full of wikis,
but we do it because it has other substantial advantages. However, we
shouldn't assume that every would-be author is comfortable using pull requests.

This change presents the edit-on-github interaction as the most straightforward
one, suggesting that advanced users may which to check out locally.
Merge pull request #750 from silverstripe-rebelalliance/open/5971

FIX If ClassName read from DB doesnt exist, dont break
Add reference for  template documentation
Merge pull request #755 from wilr/doc/template-top

Add reference for TOP in template documentation
FIX: ensure date input has a date picker to trigger open (#7504)
Merge pull request #757 from wilr/trac/7504

FIX: ensure date input has a date picker to trigger open (#7504).
BUG Fix wrong date conversion from PHP format 'y' to jquery date and back.

While 'y' in PHP means 4 digits year (e.g. 2012), jquery date picker means 2 digits (e.g. 12). That's all fine until then but when you pass the 2 digit year value back to PHP it all goes awry.
For exmple, defatult date format in en_US is 'MMM d, y' so in jquery date picker it's something like this 'Aug 22, 12' and eventually PHP will convert that value to '0012-08-22' which completely wrong.