Complete sandbox with "in person" vote

[leio10]

This PR implements the "in person" vote in the sandbox.

It also fixes some issues we had in the sandbox:

• It improves a bit the design consistency.
• It allows to select several answers for a question.
• If fixes a bug with the "encrypt" button (it was opening a new tab when pressed).
• If fixes the stress tests buttons, that weren't working.
• It checks the result of the casting of the vote in the BB server (asks for the status of the pending message).

[codecov-io]

Codecov Report

Merging #172 (26567fe) into feat/in-person-vote (c66452d) will decrease coverage by 0.45%. The diff coverage is 10.86%.

@@                   Coverage Diff                   @@
##           feat/in-person-vote     #172      +/-   ##
=======================================================
- Coverage                69.83%   69.37%   -0.46%     
=======================================================
  Files                       91       91              
  Lines                     1485     1499      +14     
=======================================================
+ Hits                      1037     1040       +3     
- Misses                     448      459      +11     

Impacted Files	Coverage Δ
...er/app/controllers/sandbox/elections_controller.rb	0.00% <0.00%> (ø)
...ard/server/app/helpers/sandbox/elections_helper.rb	45.00% <41.66%> (+2.14%)	:arrow_up:

---

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 c66452d...26567fe. Read the comment docs.