Include license texts in persisted datamodel json file

[ohecker]

As a user of Solicitor I want to make sure that I can reproduce Solicitor report results completely by regenerating the reports based on a previously stored data model json. This is currently limited by the fact that license texts are not stored in the data model json but are always (re-)fetched based on their URL.
The content fetched via URL is stored/cached locally in the filesystem. So to safely reproduce reports it is currently necessary to not only save the data model json but to also archive this file cache.

License texts should be included in the data model json to only require this to be archived.

[ohecker]

Implementation should avoid excessive file sizes of the data model json by ensuring that identical license texts are stored only once in the file.