Axon HTTPAPI tweaks

[vEpiphyte]

Changes from #1817 based on integration feedback:

• Use a hashset in the axon httpapi handler for uploading a file so all the hashes for the given file are made available to the user.
• Rename HTTPAPI handlers to be more descriptive.
• Add $lib.bytes.has() stormtypes api
• Add a /has HTTPAPI for axon
• Small Axon doc updates

[codecov]

Codecov Report

Merging #1822 into master will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1822      +/-   ##
==========================================
- Coverage   96.25%   96.23%   -0.02%     
==========================================
  Files         139      139              
  Lines       27249    27266      +17     
==========================================
+ Hits        26228    26239      +11     
- Misses       1021     1027       +6     

Flag	Coverage Δ
#linux	96.23% <100.00%> (-0.02%)	⬇️
#linux_replay	66.42% <54.16%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
synapse/axon.py	99.11% <100.00%> (+0.04%)	⬆️
synapse/lib/stormtypes.py	97.39% <100.00%> (+<0.01%)	⬆️
synapse/lib/spawn.py	95.48% <0.00%> (-1.94%)	⬇️
synapse/lib/base.py	91.96% <0.00%> (-0.90%)	⬇️
synapse/lib/agenda.py	94.11% <0.00%> (-0.23%)	⬇️
synapse/lib/lmdbslab.py	98.76% <0.00%> (+0.41%)	⬆️

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