Use tab-persistence to open filter example searches on the help page

[khituras]

The help page offers links to example searches. For the filter examples, there are always two examples, one with disabled and one with enabled filter. Currently, there is a warning not to open the links too quickly one after another because this would screw up result display (the single state would always return the latest search result).
If tab-persistence is working properly (fix #202 first), use it to open different "internal tabs" for the two searches.