Automatically choose next validator from propose queue

[TheoXD]

This PR makes it so that deploys get into a block faster (within 1 minutes rather than 15 minutes) by automatically choosing one of the next two validators from the propose queue by using this API https://status.rchain.coop/api/validators. Finalization still takes quite a bit of time so improvement may not be significant. All that is required from the user is to switch to mainnet. Switching back to any other network pauses the autoselector. When mainnet is enabled, Transfer and Deploy buttons are disabled during the first fetch, so that user doesn't use a manually selected node. For convenience there is a checkbox to manually disable this behavior too.