This commit changes how the word frequency and cost data is
represented in memory. Previously this data consumed about 7 MB on all
Metabase instances. This commit lowers that memory to roughly 1.5
MB. The primary change is storing the hash of the strings in a
primitive integer array instead of the strings themselves. It also
stores the cost in a correlated primitive double array, saving space
there as well.

When test pulses are sent out their channel_types are strings not
keywords which caused the multimethod lookup in the pulse code to
fail. This commit adds a unit test that covers our pulse test
capability and ensures channel_type fields are keywords before
invoking the multimethod.

Fixes #6465

Previously the creator of the alert would be notified, but any
recipients added to the new alert were not being notified. This commit
continues to notify the creator, but then will let all of the other
recipients know that they've been subscribed to an alert.

Previously whenever an alert was deleted it would notify the creator
of the deletion, even if the creator was the one that did the
deleting. This commit changes that behavior to only notify if the
creator is different from the user deleting the alert.

Previously alerts were showing up as pulses. This commit adds a
distinction between pulses and alerts

Previously the code would only allow a string literal for a
description. This poses problems for i18n strings, i.e. `(tru "my
string")`, which evaluates to a string, but at macro expansion time is
not a string. This removes that precondition. The string is still
validated at runtime via schema.

By default Druid weeks start on Monday, but the rest of Metabase
expects that the weeks start on Sunday. This commit adds an `origin`
clause to `week` granularity queries which will force Sunday as the
start of the week.

Fixes #6047

Not sure when it was added, but Redshift now supports specifying a
timezone. It looks like Redshift has a similar bug to Oracle for unix
timestamps (written up as #5789) in that it's interpretting the UTC
timestamps as in the report timezone already, rather than adjusting.

Fixes #6279

Previously notifications of alert lifecycles (i.e. subscribing to an
alert, or being removed from an alert) was happening on the HTTP
request thread. When the SMTP server was slow, this would slow down
the response and thus the UI. This instead returns immediately and
connects to the SMTP server via a background thread separately from
the HTTP request thread.

This commit has the backend code needed to support alerts. From the
frontend perspective, Alerts is separate from pulses and has a
different endpoint, however much of the backend code and database
tables are shared. A few new columns were added to the pulse table to
support alerts, but most of the data is the same between pulses and
alerts.

This also adds several "meta-notifications" around alerts to let users
know when they've been added to an alert, removed from an alert or if
a question has changed such that the alert is no longer meaningful.

This fixes #1372, fixes #6261 and fixes #5768.

* MetaStore integration

* Fix lint error

* restructure embedding levels

* Rename updateSetting in setting widgets to onChange, add onChangeSetting

* embed flow images / spacing

* lint fix