Add random messages service to the question view

Refactor the input number validation.
Extract repeated code in the practice service into a common
method, add the repeat tag filter.
Merge remote-tracking branch 'upstream/master'
Fix skills paddings, fix grunt sass path

Fix both skill used and skills to review paddings and margins.
Merge pull request #26 from mlopez-firstfactory/master

Refactor the input number validation. Extract repeated code in the practice service into a common method, add the repeat tag filter.