RTL support and Persian translation

[sineau]

This PR contains the following:

• Persian translation,
• RTL styles (including Bootstrap),
• functionality to switch to RTL style based on locale,
• locale numbers in various views

Please note that for cases where I need to decide based on locale (particularly for styles and time input in topic creation view) I used 'fa' only, although I think I should've added Arabic and Hebrew as well. (In memory of @ashkang)

[franciclo]

@sineau thanks this contribution! We will be making a review shortly. Can you rebase your branch with development?