#815 Add mwoffliner options to deal with warning templates

[Nemo]

Story: as a ZIM distributor, I want to be able to choose what level of confidence/extensivity to require from a wiki. For instance, I may want to do one or more of the following:
a) hide superfluous templates asking further edits which can't be provided offline, like {{stub}} and friends;
b) hide "ugly" warning templates about severe content issues e.g. with NPOV/libel, copyright violations;
c) remove entirely any page containing (b) [or even (a)] to avoid issues.

== Current situation ==

In wikipedia_it_all_06_2014.zim I see a) and b) mostly done (though with some problems, https://sourceforge.net/p/kiwix/bugs/715/ https://sourceforge.net/p/kiwix/bugs/712/ ), while c) is not done. For instance there is a [[Roberto Fiore]] page, empty because its only content on the wiki is a legal warning.
This is ok, though personally I'd prefer b) templates to be left and at least some mirrors will have problems without c).

== Future ==

After the infrastructure for mass ZIM generation is ready, however, it will be nice to document how templates for a) and b) are selected so that editors are clearly delegated to tag them as needed. In the past there was some resistence sometimes, but Kiwix can't continue working in the wikis' stead when they become hundreds.

Additionally, any Wikimedia chapter or other "at risk" organisation willing to distribute ZIMs, especially commercially, will probably need c). (Legitimately, this is even lower priority; we/they should pay for this feature to be developed.)