Improve UI code reusability

[tcp]

What?

It would be great if we componentize many of the UI elements we have. We repeat components in many pages and this is a golden opportunity — let's break it down and reuse them. :)

This is probably the biggest of the refactors, but it's likely to be quick.

Why?

Manage the interface better, apply changes to all places that use the same components.

This should be done in all pages -- a suggested order:

1. Users
2. Datasets
3. Infrastructure
4. Settings