Adding HX1D and HXNTU Notebook Examples

[bpaul4]

Fixes # .

• New notebook examples for 1D Heat Exchanger and NTU Heat Exchanger unit models and associated index updates
• Corrections for minor errors in index files to properly build Turbine notebook example
• These notebooks may undergo updates in the future regarding the outcome of Standardize naming in Heat Exchanger models idaes-pse#730

Proposed changes:

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[andrewlee94]

Looks good - most of my comments are minor things.

I made a few requests on the HX0D notebook that are also applicable to the other notebooks (I didn't repeat most of them to keep things shorter).

[MarcusHolly]

I didn't see a reason to add a separate example for the shell and tube 1D example since there seems to be significant overlap with the existing heat exchanger 1D example. However, if there's something I'm missing about it or if we just want to add a separate example for shell and tube anyway, I can do that.

[bpaul4]

Thank you @MarcusHolly for picking up this PR and adding the lumped capacitance example. it looks very nice and I just have a few comments.

[andrewlee94]

One minor but important request - for the NTU example we need to clarify what MEA is to the general user. WE only need to write out the first instance in full however.

[MarcusHolly]

@andrewlee94 MEA is already specified in the problem statement.

[andrewlee94]

@MarcusHolly Ah - it is, but it is wrong. It should be monoethanolamine.