Summary

Closes: #597

This PR add support for custom minimum required voting power for offchain voting.

Until now, we allowed anyone with voting power > 0 to cast the vote, and it'll just fail on the backend with an error.

With this PR, we will validate the voting power before allowing user to cast the vote, preventing user frustration and unnecessary actions.

How to test

Go to snapshot.org, and create some proposals with the following conditions (need to edit space settings before creating each proposals):

A. A regular proposal, with basic voting validation (anyone with non-null vp can vote)
B. A proposal with custom minimum voting power (need at least X vp to vote)

Now, try to vote on each of these proposals, by opening the vote modal.

In case of A:

1. you should be able to vote if your account has vp > 0
2. if your vp === 0, it should show the warning message that you don't have enough vp, and disable the voting form

In case of B:

1. When your vp === 0, it should show the warning message that you don't have enough vp, and disable the voting form
2. When your vp > 0, but < X, it should show that you need at least X vp to vote, and disable the voting form
3. When your vp >= X, you should be able to vote