Allow HashMap to map to an Interface

[fubuloubu]

Closes: #1824

What I did

• Refactored "Factory" example into new example "TokenSwap"
• Updated some of storage variables to use Interfaces directly (other than exchange HashMap)
• Updated some comments
• Refactor to use imported interfaces (waiting on Error with Mutual importing when interfaces are used as a variable #2107)
• Refactor to allow HashMaps to map to Interfaces
• Update exchange HashMap to use Interfaces (waiting on parser/ refactoring)
• Refresh test suite for "TokenSwap"

Cute Animal Picture

[codecov-commenter]

Codecov Report

Merging #2048 into master will decrease coverage by 38.27%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #2048       +/-   ##
===========================================
- Coverage   84.95%   46.67%   -38.28%     
===========================================
  Files          83       83               
  Lines        8333     8332        -1     
  Branches     2012     2012               
===========================================
- Hits         7079     3889     -3190     
- Misses        752     3897     +3145     
- Partials      502      546       +44     

Impacted Files	Coverage Δ
vyper/parser/events.py	7.04% <0.00%> (-86.62%)	⬇️
vyper/parser/s_expressions.py	5.88% <0.00%> (-85.30%)	⬇️
vyper/ast/natspec.py	14.81% <0.00%> (-83.96%)	⬇️
vyper/cli/vyper_json.py	10.40% <0.00%> (-74.40%)	⬇️
vyper/cli/utils.py	18.42% <0.00%> (-73.69%)	⬇️
vyper/parser/external_call.py	10.00% <0.00%> (-73.34%)	⬇️
vyper/signatures/event_signature.py	25.53% <0.00%> (-70.22%)	⬇️
vyper/compiler/output.py	34.31% <0.00%> (-65.69%)	⬇️
vyper/signatures/sig_utils.py	35.71% <0.00%> (-64.29%)	⬇️
...er/function_definitions/parse_internal_function.py	35.64% <0.00%> (-62.38%)	⬇️
... and 53 more

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[codecov-io]

Codecov Report

Merging #2048 (13458fe) into master (5db35ef) will increase coverage by 0.02%.
The diff coverage is 86.36%.

❗ Current head 13458fe differs from pull request most recent head 2a42e56. Consider uploading reports for the commit 2a42e56 to get more accurate results

@@            Coverage Diff             @@
##           master    #2048      +/-   ##
==========================================
+ Coverage   85.70%   85.72%   +0.02%     
==========================================
  Files          90       90              
  Lines        8765     8780      +15     
  Branches     2091     2097       +6     
==========================================
+ Hits         7512     7527      +15     
+ Misses        762      761       -1     
- Partials      491      492       +1     

Impacted Files	Coverage Δ
vyper/parser/expr.py	76.34% <80.00%> (-0.42%)	⬇️
vyper/parser/external_call.py	85.43% <85.71%> (+1.06%)	⬆️
vyper/types/types.py	82.58% <85.71%> (+0.17%)	⬆️
vyper/parser/global_context.py	71.42% <100.00%> (ø)
vyper/parser/stmt.py	83.33% <100.00%> (+0.12%)	⬆️
vyper/cli/vyper_json.py	85.20% <0.00%> (+0.40%)	⬆️
vyper/ast/validation.py	73.33% <0.00%> (+4.44%)	⬆️

---

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[fubuloubu]

Dup of #2697, closing