Add new property to Service to describe its 'mobility'

[vholland]

As @danbri said in issue #806:

Some local businesses have a nominal place-of-business but are increasingly mobile/virtual...

Increasingly, there are services like Uber, which not only have an areaServed, but the exact location of a provider is dynamic.

To that end, I propose, we add a property to http://schema.org/Service called providerMobility. It would expect a text value for now, but would allow us to differentiate this case.

[danbri]

+1 but please suggest some text values

[vholland]

Created pull request #820 with an example.

[danbri]

Fixed in http://schema.org/docs/releases.html#v2.2 - thanks all