Verifiability - show hash of encrypted vote in election detail pages

[chenchanglew]

Implementation step of Verifiability Documentation

1. frontend: show a user the hash of their encrypted ballot. (Issue: Verifiability - show vote hash after casting a vote #239)
2. smart-contract + proxy: add users' hash of the encrypted ballot (sha256) in the form. The hash will send along with the getForm to the user. (Issue: Verifiability - add users' hash of the encrypted ballot for each election. #240)
3. frontend: In the election info page, show a list of the voter who vote and their hash of encrypted votes got from the proxy. (This issue)

How:
On the election info page, show a list of the voter who vote and their hash of encrypted votes got from the proxy.

Where:
web/frontend/src/

Target:
Users can view their previously cast votes in the list.
Create paging and search for the user id, since we might have a lot of ballots. (Optional)