Minor text improvement to the database documentation.
Added possibility to add a primary key to an analysis.

This will later be used to migrate analysis to a database.
Made law analysis a primary key based data structure.

This removes the need to have the url to depend
on the name of the analysis.
Removed old code, added computation of number of documents with no text.
Improved text on eu_impact analysis and translated it to PT.

Thanks to Marta M. Matos for editing the EN version of the text.
Improved text for eu impact and added CC licence.
Fixed #9 - entity url slug field now accepts hyphens.
Changed usage of ugettext to ugettext_lazy in urls.
Added languages to settings.
Improved scheduling and analysis management.

- AnalysisManager is no longer unique: each app now
  has its own instance.
- Each app is now responsible for updating analysis on their own
  schedule.
Fixed image label.