RCFilters: Clarify 'hidden' and 'sticky' filters

RCFilters: Clarify 'hidden' and 'sticky' filters

Clarify the meaning and behavior of sticky and hidden filters
according to the following definitions:

When 'sticky' is false, the filter is saved in Saved Queries. Its
state is considered and altered by the 'Clear all filters' and
'Restore default filters' buttons.

When 'sticky' is true, the filter state is only changed using its
associated control (i.e. Number of days selector).

'hidden' simply means it is not shown as a capsule in the active
filters area.

Change-Id: I7ccb7c202e21917eb288055c509c9f904a0d01bb