Ui improvement : moved help into the action bar + ability to hide filters

++ Moved the help button to the action bar
++ Moved the edit help (pen icon) into the help pop-up (only for the main activity)
++ Added scrollbars to the main help pop-up in order to avoid cut content on small screens
++ Added a frame around the filter section
++ Ability to show/hide the filter section (hidden when the application starts)
++ Added two strings (filter title + help menu)
--- Removed two images :
   -> the pen is no longer useful,
   -> the question mark is now taken from the system in order to be displayed at the good scale in the action bar

Note :
I have been forced not to use a plural string for the filter title because the 'zero' case is bugged in Android. I used a formatted MessageFormat instead, you only have to translate the <b>bold</b> words :
{0,choice,0#<b>No active filter</b>|1#<b>1 active filter</b>|1&lt;{0} <b>actives filters</b>}

The diff files for the layouts are really messy because I changed the order of the components and the layout tree.

![filters](https://f.cloud.github.com/assets/3890441/982544/04be4b3e-07fe-11e3-993e-9f2fb29dd77c.jpg)