feat: use ObjectId for object ids in MetasysClient

[michaelgwelch]

This will be slightly easier to review one commit at a time. Only the first one is large. But 90% of it is changing type from Guid to ObjectId or converting guid to/from objectid

It was a mistake that we started using Guid for object identifiers in this library. The Metasys REST API makes no guarantee that the ids it returns will be Guids. It has never documented them as such. (For example see Get an object and examine the objectId parameter.)

This PR starts the transition away from using Guid

• Introduce new ObjectId type which has implicit conversions to/from string and to/from Guid to aid the transition to the new methods. The new type was used (instead of just using string) as I think it makes the APIs slightly easier to understand. But it also allowed us to create implicit conversions so that the changes could be made without introducing compile time breakages for clients.

• Modify all methods of MetasysClient and IMetasysClient that use Guid as an objectIdentifier to take an ObjectId instead. This is a non-breaking change due to the implicit conversion from Guid to ObjectId (unless clients are using Reflection to find methods).

• For MetasysClient and IMetasysClient methods that take an IEnumerable<Guid> we had to leave those methods. But we marked them obsolete, added new methods that take IEnumerable<ObjectId>. These new methods take their implementation from the old methods. The old methods delegate to the new methods so they are easy to delete in the future.

Future work: There are many other interfaces/methods that identify objects by Guid. This PR will be updated with those as well

• Update README to remove use of Guid.
• Alarms
• Audits
• Trends
• Spaces: Switch methods to use ObjectId instead of Guid
• Equipment: Switch methods to use ObjectId instead of Guid
• Change MetasysObject.Id return type to ObjectId
• Fix demo apps to use non-obsolete methods
• Add tests that use new methods (not 100% needed as the old methods that
  are being called just delegate to the new methods.

Note

Alarm, Audit and Activity guid identifiers will be left alone (for now). While those are also just documented as strings it just increases the scope of the change to be too large. So only Object identifiers are being targeted at this time. See #142 for the alarms and audits changes.

[michaelgwelch]

This test was removed because it represents a condition that can't happen any more. We can't fail parsing a guid since we no longer attempt to parse to guid.

[michaelgwelch]

To test for null we need a JSON null which looks like null vs. a string with the word null which looks like "null". The previous version of this test was just encoding the word "null" as a string.