Multichain token census [Onvote]

[jpaulet]

In the Onvote theme, add a new census type that represents a "Multi-chain" token census, allowing to easily create a multichain census.

Todo:

• Create the new tab for the multichain as the design
• Create the Census3 strategy that represents the token in each available network
• When pasting the first token address in any input, show the "Use the same address.." checkbox. If the user selects the checkbox, paste the same address to all the other inputs.
• Allow the organizer to select between "1 vote" or "Combined weight", that sums all the tokens that the holder owns regardless of the network.
• Create the new voting process and test it