Make issue, MR and issue board filters persist between visit

Description

If you're using a particular filter, it's convenient if it persists between visits.

Proposal

1. make it easy to clear filters, so that it's not annoying that the filters persist
2. make MR filters persist between visits
3. make issues filters persist between visits
4. make issue board filters persist between visits

Links / references

cc @jschatz1 @iamphill