Issue title: MRTK 2.2 - Spatial Mapping starts automatically
 Issue body: ## Describe the bug

Updated to Mrtk 2.2 and now realizing that I cant disable spatial mapping at the start. I can disable it on runtime, but the checkbox under `Spatial Awareness System Settings > Spatial Mesh Observer Settings > Startup Behavior` is not working.

## To reproduce

Steps to reproduce the behavior:

Set under `Spatial Awareness System Settings > Spatial Mesh Observer Settings` the value of Startup Behavior to `manual start`.

## Expected behavior

Should not start. Only start if I trigger it in runtime.

## Screenshots

![image](https://user-images.githubusercontent.com/15002527/70919776-c1768100-2021-11ea-929a-10cf066b1d8d.png)

## Your setup (please complete the following information)

- Unity Version 2019,3
- MRTK Version v2.2

## Target platform (please complete the following information)

- HoloLens

## Additional context

Recreated my profiles; ported via guide;

 Comments: 
 Comment 0: This worked for me; I outcommented under Assets\MixedRealityToolkit.Providers\WindowsMixedReality\WindowsMixedRealitySpatialMeshObserver.cs in line 147
```
        public override void Enable()
        {
            //if (!IsRunning)
            //{
            //    Resume();
            //}
        }
```
{'source': 'GithubIssues', 'repo_name_with_owner': 'microsoft/MixedRealityToolkit-Unity', 'issue_id': 538487846, 'repo_stars': 2952.0}