Support tab overrides

Created by: slifty

We have a use case where different stages of proposal might have different sets of tabs / information.

The current architecture allows us to override the wiki tabs for entries, but has no concept of different types of override for different types / stage of entry.

After chatting about this with @frankduncan we landed on the following approach:

Creating a $wgLFCExtraTabOverrides global which is a dictionary.

The keys of the dictionary are flags which can be included in a an entry's page to indicate that it should use the corresponding override tab list. An entry / page can indicate which tabs to use by including something like <!-- TABS: {key goes here}--> (specification TBD as part of this issue)

This will involve updating lfc-analysis-rule.php