[WIP][Feature] multi network local config

[mirceanis]

What's here

This changeset deprecates the global mutable Networks object in favor of locally configured MultiNetworkConfig instance(s)

Local configurations are potentially lighter-weight and don't overwrite each other.
Future versions will completely remove the default infura URLs as well, and local configurations will be a necessity then.

Also, this paves the way to non-JsonRPC based ethereum providers and to true multi-platform.

A an added bonus, the default MultiNetworkConfig allows networks to be indexed both by networkID and by name.

Testing

Methods have been added to check all known paths of interaction with the multi-network configuration holders.

The deprecated Networks object now implements that same interface and all existing tests have been kept.

[codecov]

Codecov Report

Merging #4 into develop will increase coverage by 0.49%.
The diff coverage is 100%.

@@              Coverage Diff              @@
##             develop       #4      +/-   ##
=============================================
+ Coverage      38.64%   39.14%   +0.49%     
+ Complexity        16       10       -6     
=============================================
  Files             14       15       +1     
  Lines            370      373       +3     
  Branches          36       36              
=============================================
+ Hits             143      146       +3     
  Misses           216      216              
  Partials          11       11

Impacted Files	Coverage Δ	Complexity Δ
...in/java/me/uport/sdk/core/NetworkConfigurations.kt	100% <100%> (ø)	0 <0> (?)
core/src/main/java/me/uport/sdk/core/Networks.kt	86.44% <100%> (-1.62%)	2 <1> (-6)

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