Require licenses use an SPDX licence identiifer

[jamietanna]

As noted in #223, licenses are a little awkward to make read easier, because we've got them in differing formats.

To make this easier, we should manage them purely through their SPDX License identifier i.e. ISC for the ISC License.

This then allows us to render more human-readable content, linking out to the original license, etc.

Current licenses in use

""
https://osdatahub.os.uk/legal/termsConditions
"This API can only be used where there is a legal basis to do so. Make sure you have a valid use case before you go too far with your development. You must do this before you can go live."
"This API uses the Application-restricted pattern.  For more information on this pattern, please see our Security and Authorisation page <https://digital.nhs.uk/developer/guides-and-documentation/security-and-authorisation#user-restricted-apis> within the NHS Digital Portal."
"This API can only be used where there is a legal basis to do so. Make sure you have a valid use case before you go too far with your development. You must do this before you can go live (see ‘Onboarding’ below)."
"This API can only be used where there is a legal basis to do so. Make sure you have a valid use case <https://digital.nhs.uk/services/summary-care-records-scr/viewing-summary-care-records-scr#scope-of-viewing-scrs> before you go too far with your development. You must do this before you can go live (see ‘Onboarding’ below)."
"[statistics.gov.scot](statistics.gov.scot) provides public access to the data behind Scotland's official statistics in linked open data format.\n\nThe SPARQL endpoint allows flexible querying of the datastore using the SPARQL 1.1 language.\n\nThis API can be used to extract data, automate report-writing, publish data visualisations, or make interactive tools for exploring the data.\n\nThe site is managed by the Scottish Government on behalf of all producers of Scottish official statistics including Scottish Government, National Records of Scotland, NHS Information Services Division, Visit Scotland and others.\n\nThe API is provided under the Open Government Licence with no requirement for registration.\n\nFor queries or comments, please contact [[email protected]](mailto:[email protected])"
ISC
https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/
"subscription required"
https://epc.opendatacommunities.org/docs/copyright
"Licenced per dataset, but mostly OGL "