Add option 'adhocracy.monitor_pager_clicks'.

Will be used to (de)activate monitoring of pager clicks.
Log the list index and active sort of pager clicks

When a user clicks a proposal the list index and active sort are logged
into a cookie. On the next page load, this cookie is read and the data
is send to the stats controller. The option
'adhocracy.monitor_pager_clicks' must be set to True to enable the
functionality.

This is needed for hhucn/adhocracy.hhu_theme#119.
Make page stats baseurl always available.
Remove dependency between on-page ping and pager click stats.
Correctly check for element existence.
Use jQuery.isEmptyObject to check whether properties are set.
Add comment to cookie deletion.
Use RegEx literal instead of a string.
Merge pull request #401 from wawe/feature-monitor-pager-clicks

Log the list index and active sort for clicked proposal links, JavaScript method
Remove circular import

Currently, imports of adhocracy.lib.sorting are brittle because of the circular import

lib.sorting -> lib.event -> lib.helpers -> lib.sorting
Remove the circular import
Merge branch 'behaviors' into develop
Move ValidProposalBadge validator into adhocracy form utils
Move proposal sort order selection into its own component
Add badge-specific behaviors

If the new configuration option adhocracy.enable_behaviors is enabled, user badges can be associated with changes in the UI.
The first UI change is the default sorting order.
Instead of defaulting to mixed, if the user has a badge with a sorting order behavior attached, she now gets that order.

See hhucn/adhocracy.hhu_theme#121 for details.
Add space in user/edit form for HTML validity
Intercept setdefault and pop calls in cookie session implementation (Fixes hhucn/adhocracy.hhu_theme#304)
Commit after creating a treatment (Fixes hhucn/adhocracy#303)
Merge pull request #403 from phihag/behaviors

Add badge-specific behaviors
propose_login returns true if login is missing.
Fixed documentation error updated version of staticlxml to newer one that is still available