[GROUND-23] De-relationalize Cassandra schema

[seanlobo]

I encapsulated some tables via Cassandra set and map collections. This uses fewer reads when accessing the data, which should be best practice.

[vsreekanti]

The Travis CI build failed. @seanlobo, you can see the failing tests here.

[codecov-io]

Codecov Report

Merging #72 into master will decrease coverage by 0.15%. The diff coverage is 85.84%.

@@             Coverage Diff              @@
##             master      #72      +/-   ##
============================================
- Coverage      85.1%   84.94%   -0.16%     
- Complexity      626      637      +11     
============================================
  Files           115      115              
  Lines          3027     3083      +56     
  Branches        223      222       -1     
============================================
+ Hits           2576     2619      +43     
- Misses          405      419      +14     
+ Partials         46       45       -1

Impacted Files	Coverage Δ	Complexity Δ
...cassandra/CassandraLineageGraphVersionFactory.java	100% <100%> (+2.43%)	5 <0> (-1)	:arrow_down:
...ns/cassandra/CassandraVersionSuccessorFactory.java	94% <100%> (+1.14%)	10 <3> (+3)	:arrow_up:
...models/cassandra/CassandraGraphVersionFactory.java	100% <100%> (+2.7%)	5 <0> (-1)	:arrow_down:
...s/cassandra/CassandraVersionHistoryDagFactory.java	100% <100%> (ø)	12 <1> (-2)	:arrow_down:
app/db/CassandraResults.java	81.48% <33.33%> (-13.76%)	13 <2> (+2)
app/db/CassandraClient.java	88.61% <80.35%> (-6.91%)	21 <6> (+10)
...ls/cassandra/CassandraStructureVersionFactory.java	94.59% <90.9%> (-0.41%)	6 <0> (ø)

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[vsreekanti]

Will merge this after porting the Cassandra schema over.