Add visualisation of posting frequency
As part of #534 (closed), I want to make it easier to visualise how often I post content, of all content types.
For now, look at it in terms of:
- per hour
- per day
- per day of the week
- per month
And will see if there are any other interesting pieces of data I want to present in the future.
This requires generating the actual counts of data, which I can do using a custom output format's template, and then render it using Chart.JS.
Plus, add an announcement post.
Closes #534 (closed).