[Sensor] Visualize the semantic observations

[bigbike]

Motivation and Context

As titled.
This PR adds a brand new functionality to visualize the observations from the semantic sensor.

The results are as follows:

How Has This Been Tested

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have completed my CLA (see CONTRIBUTING)
• I have added tests to cover my changes.
• All new and existing tests passed.

[bigbike]

@mosra:
I was thinking the wrapping of the colorMapTexture found here.
I believe for depth rendering it should be set to ClampToEdge while for semantic rendering it should be set to Repeat. How do you think?
(Update: I just changed the code above.)

[bigbike]

@mosra:
Another question: we can clear the depth, clear the color, but how can we clear the objectId (another color attachment)

[mosra]

use the clearDepth() / clearColor() APIs on the framebuffer, instead of clear(), those allow you to clear also non-integer attachments