UX problems to be fixed pre-release

[jomuel]

Some problems I noticed while testing/restoring the mainnet wizard:

• Kyber and Uniswap transactions take unusually long and sometimes even time out (timeout is set to 120 seconds). Tweak settings to fix this. (related issue: Check Configuration of DEX transactions and optimize #99)

• Timeout of Kyber/Uniswap transactions is not handled. The web interface just gets stuck. Proposed fix: Redirect to the launch page and add a message that the transaction was not successful yet, with a link to the transaction on Etherscan.

• Web3 exceptions on contract calls are also not handled and cause the web interface to get stuck. Did not occur on mainnet, but during token minting on Goerli.

• Transaction fees are not taken into account when obtaining tokens from exchanges. If the user orders the 6 RDN and 2 SAI that are required to launch, he will end up with 5.9 odd RDN and 1.9 SAI.

• If the user clicks on the three buttons to obtain the different assets ("Send 0.02 ETH", "Exchange ETH for RDN", "Exchange ETH for SAI"), he will end up with not enough ETH to start Raiden after part of it has been used to acquire RDN and SAI. Proposed fix: Add a "Send 0.05 Eth" button and advise the user to use that if he wants to use the exchanges.