Renamed UncertainChunk to Uncertain

[NoahCardoso]

I renamed the UncertainChunk datatype to just Uncertain as part of the renaming chunks named in the form "XChunk" as just "X".
Contributes to #3244

[samm82]

Based on @JacquesCarette's comment, since "Uncertain" is also an adjective, we may want to think of another name for these chunks as well. Perhaps investigating the difference between UncertainChunk and UncertQ would help shed some light on this!

[NoahCardoso]

@samm82 would changing UncertainChunk to Uncertainty be better? Also do you want all of the Chunks to be nouns? I changed ParameterChunk to Param, UnitalChunk to Unital, UnitaryChunk to Unit, and CodeChunk to Code.

[JacquesCarette]

Now is our opportunity to think a bit deeper: UncertainChunk is the encoding of a ConstrainedChunk that adds an uncertainty field to it. It isn't "an uncertainty".

The problem with coming up with a good name for it is that it is likely to require coming up with a new better name for ConstrainedChunk first!

So there's a bigger issue (which you should probably get @samm82 and @balacij help you draft) about naming all things derived from Quantity.