Support fulltext search by trigger name and patterns

[beevee]

Before the introduction of pages in trigger list (moira-alert/web#14), users could find their triggers with a simple page search in their browsers (Ctrl+F). Now it is impossible, and finding triggers on multiple pages became hard.

We should introduce a replacement for trigger selection window and combine it with a fulltext search in a single search string that supports #tags.

Companion issue for moira-web is moira-alert/web#48