Configuring Logging Level in Operations Guide was missing a TOC entry.

This wraps some uses of `{{}}` which was rendering ``` entities directly in the document with `{% raw %}` opening and closing tags.

It also adds a line break that was missing, causing the new paragraph to be rendered as part of the previous bullet point.

Attach them attachment images 

This was moved to the operations guide.

Docs show the usage of VisualVM for local and remote (via JMX)
monitoring of a Metabase instance.

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.

Since the metabase-deploy repo seems to no longer get updated, the instructions listed here won't work anymore. Unfortunately Heroku does not offer re-deployments. Adding an empty commit and pushing fixes the problem.

Adding a note about restrictions on subnets that apply to ELB and RDS, slightly more nuanced than "just check all the boxes". See http://discourse.metabase.com/t/cannot-setup-on-aws-in-vpc/2166 for more detail.