Strip mentions and html from input used for the search index
We should introduce a new column for search tsvectors and ensure the content converted to tsvectors has it's html and mentions stripped beforehand. This will lead to more accurate matches and an ability to actually make remote profiles unsearchable for unauthenticated users (right now we restrict the user search to not show remote users to unauthenticated users, but if a local user mentioned them in a post, the result will be displayed)