Add new dashboard functionality

[jacobschultz]

These task is relatively open ended, but should be used as a guide. When referring to the 'dashboard', we are referring to the first page in scout a user sees after logging in. Today, all that is shown is device counts for all of the platforms scout manages, plus a count of the servers. We'd like to have a configurable grid of items with useful information below these counts. Some ideas of what that could be include:

1. Viewing the counts of devices in saved reports (Required for PR)
2. View health check information from various servers
3. View the count of users in scout
4. View scout server information
5. View frequency of cron jobs executions
6. View scout total device count over time

Tasks:

1. Add a new database column to the reports called 'show_in_dashboard' that is of boolean type
2. In the report create / edit view allow the user to check this new box to show this saved report in the dashboard
3. Import a charts library like chart.js to be used in dashboard visualizations.
4. Add a new endpoint to get the saved reports and their results to load into the dashboard
5. Upon page load, show some charts of the saved reports in the dashboard.
6. Implement any of the other ideas above.

PR Ready When:

1. Reports can be created / saved with the 'show in dashboard' checkbox checked
2. On the dashboard you are able to view the device counts in the various reports
3. BONUS: One or more of the other ideas