Present a POI (proof of indexing) when opening an allocation

[abarmat]

This PR is built on top of rebased changes from #475

[codecov]

Codecov Report

Merging #544 (84f63b4) into dev (cf8b7d8) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #544      +/-   ##
==========================================
- Coverage   91.19%   91.14%   -0.06%     
==========================================
  Files          37       37              
  Lines        1795     1784      -11     
  Branches      293      293              
==========================================
- Hits         1637     1626      -11     
  Misses        158      158              

Flag	Coverage Δ
unittests	91.14% <100.00%> (-0.06%)	⬇️

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

Impacted Files	Coverage Δ
contracts/staking/Staking.sol	98.97% <100.00%> (-0.03%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 726562c...84f63b4. Read the comment docs.

[pcarranzav]

This PR has become quite outdated and would need a big refactor to get merged. I'll close it and we can use it as a reference for a new PR if the corresponding proposal is reactivated.