Offer a way to extend/overwrite OKH data

[hoijui]

... for krawled platforms where the data comes from the API (e.g. Wikifactory and Thingiverse).
(vs. platforms where it comes from a project-supplied file (e.g. okh.toml on github and gitlab))

This issue arose out of OKH-LOSH#129.

Reasoning

One of many reasons we would want that, is visible in the following example:

For several reasons, it can be paramount to have a (platform independent) way to contact the author,
and that is most naturally by email.
Platforms like Wikifactory do not allow us to get the project authors email, so we can not put it into a projects OKH data.
If the krawler checks if such projects have okh.toml files hosted, and uses them if yes, these projects would still have a way to supply an email (among any other meta-data that the krawler can not get form the platforms API).