Set up an incremental compiler

[bebraw]

The idea would be to check an earlier compilation (hash against the JSON files?) and avoid compilation when possible. The current design already allows this but extra logic is needed.

[bebraw]

The general strategy for this is as follows:

1. Get changed files from Git
2. Return only routes that are affected - this means checking components usages in components and layouts (a big check!)
3. Pull earlier build (zip) and generate the changed routes on top of that
4. Store the build (zip)

Likely the easiest way to deal with the zip is to include it to the site itself. In case it's missing, a full build should be performed.