Capture TOS agreement in store

[ebekker]

Add fields for:

• createTosAgreeDate - timestamp when TOS were agreed upon message create
• createTosAgreeVers - version of the TOS which were agreed to (i.e. a URL)

In order to preserve the version of the TOS that was agreed to, we can form it as a URL similar to:

https://raw.githubusercontent.com/ebekker/FMRL/{GitHubCommitHash}/FMRL/Shared/TosContent.cshtml

Addtionally, if and when we add storing a receipt record, we can add a comparable set of readTosAgreeDate and readTosAgreeVers fields to the record.