Fine-grained permissive license detection: public-domain-like licenses, notice-required licenses

[pilosus]

For now, we lump all "permissive" licenses into one type Permissive.
A user may want to differentiate between

1. Licenses that require preserving copyright notice, i.e. attribution (like Apache-2.0 or MIT)
   They may require a prominently visible copyright notice.

2. Public-domain-equvalent licenses (like WTFPL, CC0, 0BSD). They are:

• require no attribution
• public-domain is a complex topic, legislation-dependant, there may be problems qualifying a software give away to the public domain at will in Continental Europe at least (so that the copyrights may hold)
• can be susceptible to paten trolling

We may split Permissivetype into PermissiveNotice and PermissivePublicDomain respectively.