Show rule description in rule page

[vincent-olivert-riera]

Before, when you wanted to see the description of a rule, you needed to edit it in order to load the form and then look at the description field. That was a little bit weird and could be considered as an anti pattern for good usability.

Now, since we have added the description to the rule_dict template tag, it is displayed in the rule detail page.

[vincent-olivert-riera]

Rebased on master with fixup commits squashed:

• I have amended the commit message accordingly
• I have fixed the position of the if to only wrap the description block and not the whole panel body.