Make Central Store to keep track of pending transactions

[lsaether]

Currently in Arena, the pending transactions are handled inside of the components which send the transaction. We should introduce a central store which will take a PENDING action when a new pending transaction is sent to the network. The PENDING action could trigger an alert like we have in billboard or it could open a bottom drawer similar to how it's done in uniswap. The transaction should be waited for and when it is mined it should launch a MINED action.