Merge pull request #1317 from chillu/pulls/config.php-after-statics

FIX Load _config.php's after static config manifest
FIX ConfigStaticManifest persisting access level after parsing a static
FIX Incorrect parsing of T_STRING values in class spec parsing

* Due to missing break, the T_STRING case would fall through to array.
* The values were being added to the wrong variable.
* Added missing support for missing null values.
Merge pull request #1322 from ajshort/pulls/class-spec-parsing

FIX Incorrect parsing of T_STRING values in class spec parsing
Merge pull request #1321 from silverstripe-rebelalliance/feature/config

FIX ConfigStaticManifest persisting access level after parsing a static
Missing closing <a> tag in installer
BUG Database config values aren't escaped

Causes minor UI issues if you try use database configuration values that happen to have " or other values in them.
Merge pull request #1326 from ss23/patch-1

Missing closing <a> tag in installer
Merge pull request #1327 from ss23/patch-2

BUG Database config values aren't escaped
FIX Localized HtmlEditorField Tabs

Tabs can have only lattin characters in it's name
Merge pull request #1328 from a2nt/html_tabs_fix

FIX Localized HtmlEditorField Tabs
FIX Allow FALSE in Config API, call remove() will NULL key on update()
FIX Clean cache on Config->remove()
Formatting and docs changes to configuration.md
Disable RequestHandler->handleAction() deprecation until we have fixed LeftAndMain usage
Allow for short versions in Deprecation::notification_version()
API Marked statics private, use Config API instead (#8317)

See "Static configuration properties are now immutable, you must use Config API." in the 3.1 change log for details.
MERGE More config changes