fixes#935
A bug occurs when someone requests a large amount of funds from you since the gas estimation will fail and there isn't a way of handling errors in the source yet.
This PR handles the error appropriatley for both `estimateGas` and `estimateTokenGas` where the response is only converted from hex to int if the RPC call was successful. Otherwise return the error message as the response and let the UI decide how to display it.
Currently the error for gas estimation in transaction bubbles is displayed in a popup however, ive come to realize that 2 popups open instead of one. This is a new bug of which I can't pinpoint the root cause at the moment and have opted to file a separate issue for it.
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