(Bug) changing account in Metamask doesn't affect changing the current account for executing txs in DApp

[vbaranov]

Problem: for example, if I changed the account from valid voting key to invalid, DApp still thinks that I logged with valid voting key and gives me the ability to send transactions.

Solution: implement interval to check out current account https://github.com/MetaMask/faq/blob/master/DEVELOPERS.md#ear-listening-for-selected-account-changes and save it to mobX store