Adding multi select box for the ui

[elbashandy]

Fixes

Summary/Motivation:

Adding the feature of selecting multi UnitModels in the UI

Changes proposed in this PR:

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[codecov[bot]]

Codecov Report

Merging #931 (dd56573) into main (01522d0) will decrease coverage by 0.00%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #931      +/-   ##
==========================================
- Coverage   70.32%   70.32%   -0.01%     
==========================================
  Files         576      576              
  Lines       64619    64619              
  Branches    12138    12138              
==========================================
- Hits        45446    45443       -3     
- Misses      16872    16876       +4     
+ Partials     2301     2300       -1     

Impacted Files	Coverage Δ
idaes/ver.py	61.53% <0.00%> (-4.62%)	:arrow_down:

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