Change propertyvalueconverter IsValue check for Source prop level to be string based

[MiguelGuedelha]

DB stores info as <span>XXX TIMEUNIT-STRING </span> not as a GUID so the IsValue check will always fail at the moment when checking the value at PropertyLevel => Source, and the Delivery API depends on it to succeed and proceed with its own pipeline

Fixes #188

[jcdc-bot]

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[MiguelGuedelha]

I've updated the SLN to use the proper csproj file (was still pointing to a *.10.csproj csproj file instead of *.13.csproj and enabled the delivery API in the test site as well for ease of testing

[jcdcdev]

Thank you for your contribution @MiguelGuedelha!

[MiguelGuedelha]

No worries 😄

A client wants this as part of some improvements to their headless build so was just trying to get it sorted as soon as possible