Feat: Add Block.Guid information

[iJungleboy]

I'm submitting a

[x] feature request

...about

[x] Razor templating

Current Behavior / Expected Behavior

We're about to add block information to the CmsContext #3378.

Since the ID of the block can change through export/import, there are valid use cases which would prefer to use the GUID, so we should also add a .Guid to it.

Your environment

• 2sxc version(s): 17.07