All the migrations have been updated to use BIGINTs for ID fields in the DB, but ActiveRecord needs to be told to treat those values as BIGINT as well. This PR does that.

- For some reason, :if option on before_action did not work. It got
  executed every time, returned false, and the action run anyway,
  which led to the current_sign_in_at and sign_in_count being
  updated on every request
- Return "do not filter" early in FeedManager#filter_from_home? if
  the status is authored by receiver. Usually this method is not
  called for own statuses at all, but it is called when Feed#get
  uses the database
- Return early if #reload_stale_associations! has nothing to load
  to save a database query with WHERE 1=0

* Update rails to version 5.1.1

* Run `rails app:update`

* Remove the override of polymorphic activity relationship

* Silence warning about otp_secret attribute being unknown to rails

* We will only introduce form_with where we want to use remote data

* Add inclusion validation for activity_type

* When excluding all types with `WHERE NOT IN`, the query search all rows.

* add annotate to Gemfile

* rails g annotate:install

* configure annotate_models

* add schema info to models

* fix rubocop to add frozen_string_literal

* Add exclude_types param to /api/v1/notifications

* Exclude notification types in web UI through exclude_types in the API

improved how "show more" link looks

Better initial state for unlisted/nsfw toggles