Support cumulative voting rendering

[elboletaire]

Due to the recent discovery in our explorer about unsupported voting types, we realized we should give support for the cumulative voting (a type of quadratic voting).

You can see a working election here: https://explorer.vote/process/6b342d99f2187bf87ae56dfceaf3b6531c336365830e460e212d02000000006d/1

Both the results and the envelopes views are broken due to this. Note: as said in vocdoni/explorer#121, we should first ensure we're not doing "default" renderings, to avoid issues in the future. After that, we should add specific support for cumulative votings.

Depends on vocdoni/vocdoni-sdk#408, since we don't have an easy way to identify these type of votings right now.