Cannot provide array_filter() output directly to empty() in conditional in PHP <= 5.4.

Add missing translations for “required” and “optional” strings when checking PHP extensions installed.

Fixed Language Tag Paramerters

Add missing definition for FLUSH-command

Note the tags 'spname' and spdescription' that cannot be namespaced because
their translations are loaded dynamically.

For #455 and #465

For: #458

For #454 and #465

bugfix: $langPath won't be defined if an exception is thrown by the method where we get its value from.

For #455

Also add some docs.

Fix required attributes duplication

While parsing the XML metadata file of SP, attributes in AttributeConsumerService marked as required where added multiple time causing duplication of attribute keys in attributes.required section.

"core" needs to be able to wrap some content in tabs

Replaces the need for `$this->data['htmlinject']`

Note that the flag in the context must be named 'clipboard',
not 'clipboard.js'. This is because the dot is an illegal symbol in
variable names in twig.

This module is hereby twigified. For #499.

Fixed incorrect memcache_store prefix docs.