Restructure licensing profile

[armintaenzertng]

This PR summarizes the discussion we had on the tech team call yesterday (June 27).
This moves all classes used for more in-depth modeling of licenses into the ExpandedLicensing profile, keeping only AnyLicenseInfo, LicenseExpression as well as a new SimpleCustomLicense class in the LicensingProfile.

The new structure is open to discussion. I believe some descriptions have to be rewritten.

[zvr]

I propose SimpleCustomLicense be renamed to SimpleLicensingText or something.

Then this can be used for License texts as well as for Addition texts. Otherwise, we would need a SimpleCustomAddition in the Licensing profile, which will be identical to SimpleLicense (only a string property for the text).

[goneall]

More of a request for a discussion on my comments.

[goneall]

@swinslow Some rather significant restructuring as a result of the last SPDX tech call. You can see the discussion in the minutes in the etherpad (probably not moved over to minutes yet). If you'd like to discuss real-time, just ping me and I can give you more context.

[goneall]

Thanks @armintaenzertng for creating this - overall structure looks good based on our discussion. A couple of review comments to consider / discuss.

[maxhbr]

A snapshot at a0dbc34:

[goneall]

@armintaenzertng - Pinging you on this one - can you go back through the review comments and update what you agree with and (re)comment on any outstanding?

I just bumped into this in my java code generator and would like to merge.

[armintaenzertng]

@goneall, @zvr, I implemented all outstanding change requests, please take another look.

[goneall]

Thanks @armintaenzertng

[armintaenzertng]

Found and fixed another little bug.

[swinslow]

I have a few concerns about the way this is currently addressed. I'm not going to stand in the way of merging it as a next draft, but from an initial read, these are the points that I think should be addressed prior to the actual 3.0 release:

• As currently structured, it looks like for validation purposes the only requirement is that LicenseExpression should be an xsd:string. My assumption is that it additionally would only be valid if that string conforms to the License Expression Syntax. I'm not sure how we express that in the spdx-3-model repo syntax, but I think that's an important thing for us to retain if all the pieces of the model for license combinations are being moved to a separate profile.

• Relatedly, I think part of the expression being valid is to be able to ensure that the license identifiers are valid, e.g. that any non-LicenseRef's are actual identifiers on the License List. I'm not sure whether that's feasible to do under the current structure without leveraging the ExpandedLicensing profile, if ListedLicense and ListedLicenseException are over in that profile.

• I am worried that it's confusing to have a simpleLicensingText class in the SimpleLicensing profile which is comparable to, but distinct from, CustomLicense in the ExpandedLicensing profile.

[swinslow]

On the first point above, I should note that @goneall has filed #440 to track clarifying this.

[goneall]

Per discussion with @swinslow - I'll go ahead and merge this PR and we can discuss the outstanding issues raised in the comment above after merging.