Add license stanza for 1921 Casks

Most are non-specific (category) values or `:unknown`

Anything using a GitHub/BitBucket/SourceForge URL was assumed to be `:oss`.  There could be some errors there.  Many obvious cases (eg Firefox) use `:oss` when a more specific license is available.  We will have to depend on Cask authors to make corrections to these values over time.