Squashed commits:

[ada0f09] Remove favorites from Posts table

closes #6208

closes #6014

Revert "Merge pull request #5852 from margori/3393-activity-stream-keeping-retracted-participations"

This reverts commit 096fa2dd, reversing
changes made to f7d11051.

mysql changes the type of TEXT columns to MEDIUMTEXT with "CONVERT TO",
but we don't want this, so change this columns back to TEXT.

see: https://bugs.mysql.com/bug.php?id=31291

see: https://dev.mysql.com/doc/refman/5.6/en/charset-conversion.html

Can't delete all with group/having

Add #clear_account! disable mail spec

Add migration for disabling mail for all closed accounts

Change migration to use #update_all for disable_mail attribute

Add #clear_account! false fields spec

Fix merge conflict

Dynamic row for MySQL

Set larger column index sizes

Add warning about MySQL collation

Fix database index length

This allows new databases to be created with utf8mb4, on MySQL. The maximum
column size is 767 bytes. Each character is 4 bytes long -> 767 / 4 = 191
characters for the column.

URI.extract recognized http:// as an URL, causing invalid
associations. #5347 already fixed the parsing, this just
cleans up the caches to get rid of the false associations.

* add chat_contacts table
* add chat_fragments table
* add chat_enabled column to aspects
* add chat_offline_messages table

Add Sidetiq webview to the Sidekiq monitoring panel

Add rake task maintenance:queue_users_for_removal
This basically just triggers an immediate run of the normal maintenance remove old users functionality that is normally (if enabled) scheduled to run once a day via sidetiq

Add extra safety when checking for user removal due to inactivity.
Now also user.last_seen will also be checked to make sure a user will not be removed in the event that the Devise rememember me login functionality has stopped the users remove_after timestamp from being removed.

Add initializer for maintenance job.
Add warning about mail being disabled if remove_old_users maintenance is enabled.

Fixing a .should test to expect(), adding suggested line to spec_helper to prevent the use of .should in the future

Fix for issue 5040: Adds completed_at column to account_deletions and sets timestamp upon successful completion. Depends on uniqueness of diaspora_handle when combined with person_id

* added temp. default values for user_id and item_type
* changed model validation for item_type

* changed user_id type to integer
* renamed post_id to item_id
* renamed post_type to item_type