Rewrite of the Pyomo Set component hierarchy

[jsiirola]

Fixes #326

Summary/Motivation:

This implements the rewrite of the Pyomo Set component as specified in PEP #326

NOTE: This PR does NOT switch Pyomo over to using the new Set system. Everything is implemented in parallel to the existing system. A second PR will switch Pyomo over to the new system later.

Changes proposed in this PR:

• Rewrite of Set to follow the current Pyomo component object model
• Adding "Range" objects for performing operations on continuous and discrete numeric ranges
• Adding a new approach for processing component initialization options
• Adding a new approach for providing errors for unconstructed (Abstract) component methods.

Legal Acknowledgement

By contributing to this software project, I agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov]

Codecov Report

Merging #1111 into master will increase coverage by 0.87%.
The diff coverage is 98.93%.

@@            Coverage Diff             @@
##           master    #1111      +/-   ##
==========================================
+ Coverage   69.58%   70.46%   +0.87%     
==========================================
  Files         530      532       +2     
  Lines       78478    80711    +2233     
==========================================
+ Hits        54612    56872    +2260     
+ Misses      23866    23839      -27

Impacted Files	Coverage Δ
pyomo/core/base/set.py	100% <ø> (ø)
pyomo/core/expr/numvalue.py	94.42% <100%> (+0.08%)	⬆️
pyomo/core/base/range.py	100% <100%> (ø)
pyomo/core/base/sets.py	86.58% <100%> (+0.24%)	⬆️
pyomo/core/base/block.py	84.57% <100%> (+0.88%)	⬆️
pyomo/core/base/component.py	86.92% <100%> (+0.08%)	⬆️
pyomo/core/base/util.py	100% <100%> (ø)	⬆️
pyomo/core/base/indexed_component.py	89.93% <86.36%> (-0.98%)	⬇️
pyomo/core/base/misc.py	82.83% <87.5%> (+3.8%)	⬆️
pyomo/pysp/scenariotree/tree_structure.py	83.28% <0%> (-0.23%)	⬇️
... and 14 more

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[jsiirola]

This should be ready to discuss/review. Tests all pass, and coverage is good: overall project coverage is up 0.87% and the new Set code is covered at 100%.

[michaelbynum]

This looks great to me. I even checkout out the branch and used the new sets. I created an issue for the only problem I ran into.