Refactor/remove deprecated modules

[mirceanis]

Removed the following deprecated items:

• uport-did
• UniversalDID singleton
• EthrDIDResolver legacy constructor
• legacy JWTTools.verify method

in preparation for the next major release.

If you're using any of those, the latest release that has them is 0.3.6

[codecov]

Codecov Report

Merging #46 into develop will increase coverage by 0.06%.
The diff coverage is 75%.

@@              Coverage Diff              @@
##             develop      #46      +/-   ##
=============================================
+ Coverage      72.91%   72.97%   +0.06%     
+ Complexity       216      172      -44     
=============================================
  Files             32       27       -5     
  Lines           1030      877     -153     
  Branches         159      138      -21     
=============================================
- Hits             751      640     -111     
+ Misses           188      159      -29     
+ Partials          91       78      -13

Impacted Files	Coverage Δ	Complexity Δ
jwt/src/main/java/me/uport/sdk/jwt/ECUtils.kt	74.41% <ø> (ø)	0 <0> (ø)	⬇️
.../uport/credentialstatus/UniversalStatusResolver.kt	72.72% <ø> (ø)	5 <0> (ø)	⬇️
...n/java/me/uport/credentialstatus/StatusResolver.kt	100% <ø> (ø)	0 <0> (ø)	⬇️
...main/java/me/uport/sdk/universaldid/DIDDocument.kt	64.28% <ø> (-2.39%)	0 <0> (ø)
.../main/java/me/uport/sdk/ethrdid/EthrDIDDocument.kt	60% <ø> (ø)	8 <0> (ø)	⬇️
jwt/src/main/java/me/uport/sdk/jwt/JWTTools.kt	84.86% <ø> (-1.59%)	49 <0> (-8)
...java/me/uport/sdk/ethrstatus/EthrStatusResolver.kt	89.47% <ø> (ø)	11 <0> (ø)	⬇️
.../main/java/me/uport/sdk/ethrdid/Erc1056Contract.kt	52% <0%> (ø)	0 <0> (?)
...java/me/uport/sdk/ethrstatus/RevocationContract.kt	16.66% <0%> (ø)	0 <0> (ø)	⬇️
.../src/main/java/me/uport/sdk/jwt/model/JwtHeader.kt	66.66% <100%> (ø)	6 <1> (ø)	⬇️
... and 6 more

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