Support for notifications API in KERIA

[pfeairheller]

This PR includes:

• Update to support changes to notifications API in KERIA
• Unit tests!

[codecov]

Codecov Report

Merging #63 (1876985) into development (502a2e4) will increase coverage by 1.85%.
The diff coverage is 96.70%.

@@               Coverage Diff               @@
##           development      #63      +/-   ##
===============================================
+ Coverage        41.01%   42.86%   +1.85%     
===============================================
  Files               24       26       +2     
  Lines             1992     2060      +68     
===============================================
+ Hits               817      883      +66     
- Misses            1175     1177       +2     

Files Changed	Coverage Δ
scripts/create_person_aid.py	0.00% <0.00%> (ø)
src/signify/app/clienting.py	30.69% <33.33%> (+0.03%)	⬆️
src/signify/app/aiding.py	100.00% <100.00%> (ø)
src/signify/app/notifying.py	100.00% <100.00%> (ø)
src/signify/core/httping.py	100.00% <100.00%> (ø)
tests/app/test_aiding.py	100.00% <100.00%> (ø)
tests/app/test_clienting.py	100.00% <100.00%> (ø)
tests/app/test_notifying.py	100.00% <100.00%> (ø)
tests/core/test_httping.py	100.00% <100.00%> (ø)

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