made the editor area toggle-able in `ask question` view

On our site, questions usually consist only of title. But askbot doesn't allow empty question body (there's a hard-coded limit of 10 chars). We wanted to make the body optional:

1. allowing empty body (questions with title only)
2. making the entire body editing area hidden by default, but with possibility to toggle it on (ala the Markdown preview toggle).

Nr. 1 is in a separate pull request, as I think it's universally useful to be able to set the minimum length via livesettings.

This pull request is about 2. This is *not a bug fix*; it's a feature we implemented for ourselves. I'm opening this pull request just for discussion / in case someone else finds it useful, not necessarily to be merged.

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**Askbot `ask question` page right now**:

![current](http://radimrehurek.com/no_toggle.png)

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**Askbot after this patch**:

![off](http://radimrehurek.com/toggle_off.png)

**And after clicking on the toggle link**:

![off](http://radimrehurek.com/toggle_on.png)