eth: add call to await a transaction on stellar bridge

[brandonpille]

The function bridge_to_eth (from the stellar client) allows you to convert TFT on stellar to TFT on ethereum. But this function returns once the transaction is submitted on stellar. After that the stellar-eth bridge has to recognize this transaction and act upon it: create a transaction on eth. We should add a function await_transaction_on_stellar_bridge in the ethereum client that waits until it recognizes the transaction from the bridge.

• Implement function similar to the stellar client function await_transaction_on_eth_bridge
• Fix documentation Convert TFT on Stellar to TFT on Tfchain under manual/src/v-clients/stellar)
• Add the call in the threelang examples