'Issuance Date' label should be 'Valid From'

[jchartrand]

We show the value of the credential.validFrom property in the 'Issuance Date' field, but validFrom can be a date both in the past or future and so is not the issuance date at all.

So rename 'Issuance Date' to 'Valid From'

If we did want to show the date the VC was issued we'd likely use the date it was signed.

And if we want to show the date the underlying credential (like a degree) was awarded (e.g, at convocation) then we should show a separate field called 'Awarded Date' and pull that from the OBv3 awardedDate field. That is described in: #245

Related to:

• VC with a validFrom date that is in the future shows misleading error #208
• Add awardedDate to V+ #245