CMS CSS Minor Polishing Tweaks

Fixed what I believe to be a few very minor CSS regressions, that appeared after the CSS restructure for the side-by-side preview.

- Reverted background of the right panel (and tab active state) to the slightly darker shade (as per 3.0) to keep each of the 3 panels visually separate.

- Slightly increased padding on ui-tabs-panel as felt a but too close for comfort. Had decreased since 3.0.

- Decreased padding for logged in user name in menu, felt too excessive. (3.0 was neater)

- Evened out padding above buttons in site tree sidebar

Screenshots showing changes:
3.0: http://spdr.me/xauh
3.1 before commit: http://spdr.me/jkIe
3.1 after commit: http://spdr.me/IxtB
Merge branch '3.1' of https://github.com/purplespider/sapphire into 3.1
Don't use Zend_Cache in manifests

The overhead of Zend_Cache in manifests is too high - we don't
need LRU or tags, just somewhere to dump a bunch of data that
persists

You can replace the class used by defining SS_MANIFESTCACHE
to be a class that implements the ManifestCache interface
(we can't use the Config system to set this, as it isn't
initialised yet).
API Make HTMLValue replace-able via DI

Extracted common code out to SS_HTMLValue and made abstract, then
put HTML 4 specific code in SS_HTML4Value. Its now possible to
replace HTMLValue with one designed for HTML 5 or XHTML

Requires a code change from new SS_HTMLValue to
Injector::inst()->create(HTMLValue)
Make ShortcodeParser use HTMLValue for HTML parsing
FIX Make multiple TemplateManifests not corrupt each other
NEW Let shortcodes be disabled in HTMLText & HTMLVarchar
NEW Disable shortcodes in $Layout and $Content in SSViewer
API Make default_cast Text and not HTMLText
API Make SSViewer#process return HTMLText not string

This means that you dont have to worry about casting it
as HTMLText again when using the result in a template or other context

However in some situations code might be assuming it can
check with is_string, in which case you now need to use instanceof HTMLText
Update 3.1.0 upgrading notes for casting changes
CMS CSS Minor Polishing Tweaks

Fixed what I believe to be a few very minor CSS regressions, that appeared after the CSS restructure for the side-by-side preview.

- Reverted background of the right panel (and tab active state) to the slightly darker shade (as per 3.0) to keep each of the 3 panels visually separate.

- Slightly increased padding on ui-tabs-panel as felt a but too close for comfort. Had decreased since 3.0.

- Decreased padding for logged in user name in menu, felt too excessive. (3.0 was neater)

- Evened out padding above buttons in site tree sidebar

Screenshots showing changes:
3.0: http://spdr.me/xauh
3.1 before commit: http://spdr.me/jkIe
3.1 after commit: http://spdr.me/IxtB
Merge pull request #1287 from silverstripe-rebelalliance/feature/config

Don't use Zend_Cache in manifests
Require config manifests in Core.php to avoid upgrading issues

They need to be present for the autoloader to rebuild
the manifest in the first place.
FIX Respect previous tab choices in CMS on load

Previously only worked on ajax interactions.
This makes it much easier to default the CMS to
the "list view" rather than "tree view".
FIX #8322 Use POST instead of GET when using LeftAndMain::savetreenode so large site trees can be reorganised as well
Merge pull request #1290 from patbolo/ticket/8322

FIX #8322 Use POST instead of GET when using LeftAndMain::savetreenode s...
Merge pull request #1282 from purplespider/3.1

CMS CSS Minor Polishing Tweaks