BUG Undefined `$allowed_actions` overrides parent definitions, stricter handling of $allowed_actions on Extension

Controller (and subclasses) failed to enforce $allowed_action restrictions
on parent classes if a child class didn't have it explicitly defined.

Controllers which are extended with $allowed_actions (through an Extension)
now deny access to methods defined on the controller, unless this class also has them in its own
$allowed_actions definition.
Improved docs on $allowed_actions

Added section to "Controllers" and "Form" topics,
added $allowed_actions definitions to all controller examples
BUGFIX Keep Member.PasswordEncryption setting on empty passwords

This will prevent empty passwords to set the encryption to 'none',
which in turn will store any subsequent password changes in cleartext.
Reproduceable e.g. with ConfirmedPasswordField and setCanBeEmpty(true).
Add ContentController->handleWidget() to $allowed_actions

Required by recent $allowed_actions security fix
Updated changelog
Fixed issue with cms help toggles not functioning correctly
No longer caching the target element to be toggled
BUG Transaction stub methods for better cross 2.x and 3.x compat

The transactionStart() naming is 3.x, and used by some modules
which are otherwise still 2.x compatible.

Specifically, this was added to avoid branching the payment module
into separate 2.x and 3.x compatible branches.
Update coding conventions to match SilverStripe practices
Update examples to match conventions
Correct spelling
FIX Respect tree node limits, fix search result node display

- Renamed $minNodeCount to more accurate $nodeCountThreshold
- The $minNodeCount attribute wasn't properly respected
during actual querying, so SilverStripe would always traverse
the entire tree (and load all objects into memory),
before then marking nodes as "unexpanded", which prevents
them from actually being rendered.
- Fixes nodes on search results to be expanded by default
- Fixes nodes on search results to correctly ajax-expand
Merge pull request #1289 from chillu/pulls/tree-node-limit

FIX Respect tree node limits, fix search result node display
Mark SQLite as an allowed failure until it works again
Merge pull request #1304 from simonwelsh/skip-sqlite

Mark SQLite as an allowed failure until it works again
BUG $_COOKIES is not un-magic_quotes'd

Added stripslashes_recursively to $_COOKIE (fixes #6309)
Merge pull request #1305 from ss23/patch-8

FIX $_COOKIES is not un-magic_quotes'd (fixes #6309)
BUG SQL Injection in CsvBulkLoader (fixes #6227)

Diff should speak for itself, looks like this will have to be implemented in all supported branches. 
Merge pull request #1308 from ss23/patch-10

BUG SQL Injection in CsvBulkLoader (fixes #6227)
Merge remote-tracking branch 'origin/2.4' into 3.0

Conflicts:
	control/RequestHandler.php
	core/control/ContentController.php
	dev/CsvBulkLoader.php
	docs/en/changelogs/index.md
	docs/en/reference/execution-pipeline.md
	docs/en/topics/commandline.md
	docs/en/topics/controller.md
	docs/en/topics/form-validation.md
	docs/en/topics/forms.md
	docs/en/topics/security.md
	model/MySQLDatabase.php
	security/Security.php
	tests/control/ControllerTest.php
	tests/control/RequestHandlingTest.php