Incremental feed support

RSS river polled the feeds using a period defined by 'update-rate'
parameter. But somes feeds could be requested with 'from' / 'to' date
paremeters. (i.e. it's possible to request 'only'  the new docs since a
given date).

A 2 new parameters  setup incremental feed resquests :
- 'incremental_dates' (true / false by default)
- 'start_date' (current date minus 7 days by default).

In case of incremental mode, 'url' string would be like that :

http://mywebsite/myfeed.aspx?sort_by=updated&sort_order=descending&updated_to=%s

http://mywebsite/myfeed.aspx?sort_by=updated&sort_order=ascending&updated_from=%s

The parameters sort_by, sort_order,... would change from one feed to an
other; but the %s would be always formated by using the 'updated' date
of the last  doc of the last feed page.
Incremental feed support

Store both last feed date and last downloaded doc date.
Incremental feed support

bug fixe : retrieveLastDatesFromRiver parameter were passed by 'value'
Incremental feed support

Try to use last doument updatedDate field in case _lastUpdated is not
found.
Added a web RSS river admin site

This really basic site makes possible to store default feed parameters
settings (like index and document type) and allows to create and destroy
rss river.
Restriction : one feed per river.
RssToJson : handling recursive xml object inside the Atom feed.

As a first step, RSS/Atom fields were supposed to be atomic elements
without any children. Now we want to be able to handle Atom fields
containning childrens.
Web RSS admin site : bug fix inside feeds.html view

Wrong syntax line 9
Web RSS admin site : mainly code refactoring

. REST create river building code were both in html and controllers; now
only in controller.
. bug fix: in case 'index.type' is an empty, we should not have to use
it.
. synchronous actions : loadSettings then setQuery