Implement a calendar component

[patricoferris]

There are a couple of different use cases for a calendar components that I think having a common implementation would now be useful (there's probably a library for doing it somewhere). Some use cases include:

• On the Around the Web page for events (see this todo) this would likely get #176 over the line.
• OCaml Weekly News: this could reuse exactly the same component which is detailed as a subtask in #197

I think all we need is the ability to provide the component with date-link pairs and for it to display a clickable date that takes you to an internal or external link associated with that (for example the weekly news information or the event page).

[ghost]

I imagine that we want a calendar control that supports agenda and monthly view, along with other views, and that we would default to the agenda view.

[ghost]

@patricoferris Please create use a checklist to create some subtasks. Different people might complete individual subtasks.