Add filtering API to filter proof requests by issuer-selected proof request name

[mirgee]

... and use it in integration tests.

[codecov-io]

Codecov Report

Merging #132 into master will increase coverage by 0.03%.
The diff coverage is 63.36%.

@@            Coverage Diff             @@
##           master     #132      +/-   ##
==========================================
+ Coverage   50.79%   50.82%   +0.03%     
==========================================
  Files         150      152       +2     
  Lines       22757    22826      +69     
  Branches     6017     6043      +26     
==========================================
+ Hits        11559    11601      +42     
- Misses       7639     7645       +6     
- Partials     3559     3580      +21     

Flag	Coverage Δ
#unittests	50.82% <63.36%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
libvcx/src/api/mod.rs	30.00% <ø> (ø)
libvcx/src/aries/handlers/connection/agent_info.rs	66.66% <ø> (ø)
libvcx/src/aries/mod.rs	8.67% <0.00%> (ø)
libvcx/src/disclosed_proof.rs	67.51% <50.00%> (ø)
libvcx/src/filters.rs	57.50% <57.50%> (ø)
libvcx/src/api/filters.rs	63.15% <63.15%> (ø)
...aries/handlers/proof_presentation/prover/prover.rs	48.11% <66.66%> (+2.02%)	⬆️
libvcx/src/lib.rs	33.39% <85.71%> (-0.10%)	⬇️
libvcx/src/api/disclosed_proof.rs	44.29% <100.00%> (ø)
... and 2 more

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