WIP: Restructure and Manifests

[nderjung]

This series introduces a massive restructure to kraft internals. It creates a clear seperation between a Unikraft component (whether the core, architecture, platform, library or application) and the mechanic which is used to retrieve it. This is conceptualized through a Manifest class.

In the previous structural layout of kraft, the organisation of a component was centered around the idea that it in itself is a idempotent repository. This is actually not the case, since a). internal components are not repositories and b). external repositories are not necessarily git repositories. In the latter case, the distribution of unikraft components can be streamlined by providing them, for example, as tarballs without full version history for faster retrieval and the fact that this SCM is not required for all builds.

To work around this new concept, kraft had to be reorganised in order to facilitate the existence of some component which can be (but is not always in the case of internals) retrieved by some manifest. This led to the redistrubtion of the Project class which used to encompass a working application, and the various component classes into simpler and more modular modules which can be worked individually with or without a remote source origin (via the manifest).

N.B. Due to the fact that this has been such a large restructure, many commits include a wide veriaty of changes which may not necessarily accurately reflect the full change to the file itself.

This PR is a WIP. More updates inbound.