Find the right way to parse {{#ask:}} queries

[thaider]

there are still some appearances of $wgParser that might cause problems (at least did so in the past), e.g. in 'SIDEBAR'; on the other hand the solution found in renderCustomNavigation with the local parser seems to be not very elegant...

also, there are possibly more elegant and efficient ways for the implementation in TweekiHooks::parseButtonLink()