Added new module for analysis views.
Added analysis: time series of contracts of municipalities.

For each month since 2008, counts number of contracts and their value.
Fixed error on computing the price of contracts in one analysis.
Added view and url to new analysis. Template still missing.
Added template to view of new analysis.
Improved url name of new analysis.
Added translations of new analysis.
Renamed name of analysis in main page.
Added json view of new analysis.
Removed "sites" from installed apps as it is not used.
Added rss feed to categories.
Fixed url name collision.
Added rss feed of contracts of an entity.
Fixed error: last_contracts() was showing repeated contracts.
Added absolute url and view of a contract.
Improved description of rss feed.
Merge branch 'feed', adding contract feed to entities and categories.
Added translations of new view.
Added html element to access rss. Added rss of all contracts.
Improved text of municipalities contracts time series analysis (minor).