* Add bell button

Fix #4890

* Remove duplicate type from post-deployment migration

* Fix legacy class type mappings

* Improve query performance with better index

* Fix validation

* Remove redundant index from notifications

* Add UI for enabling/disabling poll notifications

* Add poll notifications to the (advanced) quick filter bar

* Update poll notification message

“Your poll has ended” → “A poll you have voted in has ended”

* Clear up associated notifications when a poll is deleted

* Refactor uses of icons to an Icon component in web UI

* Refactor options passed to the Icon component

* Make tests work with absolute component paths

* create FilterBar componer and its container, unstyled

* introduce basic styling for FilterBar

* add selection css

* allow FilterBar to display active CSS with js

* connect the FilterBar to the Redux state

* change getNotifications to use filter

* remove temporary comments

* add an option to turn the FilterBar off in settings

* fix showFilterBar data type to boolean

* fix eslint errors

* add English and Polish translations

* allowed filter bar overflow to accomodate for longer languages

* fix mispelled translation key

* add unified CSS look

* replace text in FilterBar with icons

* add tooltips

* replace text @ with an icon

* introduce simple and advanced filtering view

* add ability to toggle the advanced view

* add Polish translations

* change Advanced View description to be more clear

* make each filter flush notifications and load new ones, fixing pagination

* simplify getNotifications once frontend filtering is not needed for FilterBar

* add a semicolon

* Revert "simplify getNotifications once frontend filtering is not needed for FilterBar"

This reverts commit 9f4be78571.

* reset filter to 'all' when turning off FilterBar