Fixing Modifying graph elements in the flowsheet

[elbashandy]

Fixes

#913

Summary/Motivation:

Cleaning up the logic of merging updates between an old flowsheet and an new one in FlowsheetDiff

Changes proposed in this PR:

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[codecov[bot]]

Codecov Report

Merging #915 (6f4a40c) into main (5f87d78) will decrease coverage by 0.00%. The diff coverage is 70.37%.

@@            Coverage Diff             @@
##             main     #915      +/-   ##
==========================================
- Coverage   70.20%   70.19%   -0.01%     
==========================================
  Files         574      574              
  Lines       64296    64285      -11     
  Branches    12127    12127              
==========================================
- Hits        45141    45128      -13     
+ Misses      16860    16859       -1     
- Partials     2295     2298       +3     

Impacted Files	Coverage Δ
idaes/core/ui/flowsheet.py	84.06% <70.37%> (-0.17%)	:arrow_down:
idaes/ver.py	61.53% <0.00%> (-4.62%)	:arrow_down:

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[dangunter]

It works! -- but with a couple of little issues. What I did was to the F101, F102 sequence in the example notebook without deleting the saved file in between. That worked quite well. Then I added this code to delete the F102 unit again:

del m.fs.s10
del m.fs.purity, m.fs.heating_cost
del m.fs.F102
TransformationFactory("network.expand_arcs").apply_to(m)
_ = vistut.initialize_model(m)

And when I hit refresh, voila, F102 goes away. There were some minor display issues though:

• I had toggled "show stream names" off, but when I refreshed the stream names showed up again; I had to toggle on/off to re-remove them
• The labels of units that I had rotated showed as rotated until I went and re-rotated them (at which point they corrected), for example:

After re-adding and re-removing F102, it still works (with above minor bugs).

[ksbeattie]

@dangunter will review