Add SMW_NS_RULE ns, refs 2273

[mwjames]

This PR is made in reference to: #2273

This PR addresses or contains:

• This is a minimal framework that allows to define a rule set and rule interpreter (out of scope for this PR). For now it has been stripped form its original implementation to only contain a bare bone to manage a rule type, its definition, and representation (as I require a structureable content type for a different PR and using the MediaWiki NS was a non starter).
• A rule page can only be edited by someone with the smw-ruleedit right (smwcurator role has the right)
• Rule types are registered with $smwgRuleTypes
• I consider this experimental

A rule definition and its content page will look like

If the content violates the schema then the user will be notified with something that appears as

This PR includes:

• Tests (unit/integration)
• CI build passed

Fixes #

[kghbln]

Placeholder pages for the wikidocu:

• https://www.semantic-mediawiki.org/wiki/Help:Rule
• https://www.semantic-mediawiki.org/wiki/Help:Rule/Type
• https://www.semantic-mediawiki.org/wiki/Help:Rule/Type/LINK_FORMAT_RULE
• https://www.semantic-mediawiki.org/wiki/Help:Rule/Type/SEARCH_FORM_DEFINITION_RULE (Add SMWSearch power profile form #3126)

Edit: Pages were now redirected to the new locations per #3431 / 2019-03-04

[kghbln]

@mwjames I suggest to adapt the offset for SMW_NS_RULE and SMW_NS_RULE_TALK to +12 and +13 respectively since the current indexes conflict with the DPLforum extension which uses them for ages, too. While we all agree that chances are low that both extensions will be installed a the same time we cannot rule this out entirely. Moreover Wikia is the most prominent user of DPLforum and I believe it will be nice to avoid potential worries from the start since you never know.

[kghbln]

The special properties are finally documented:

• schema tag
• schema type
• schema description
• schema definition

Also: schema-edit permission.

[krabina]

note: in the examples above, LINK_FORMAT_RULE must be changed to LINK_FORMAT_SCHEMA