QoL: oasis paratime show should support Ethereum transaction IDs (with optional 0x prefix)

[CedarMist]

To improve quality of life it would be good if either the Oasis transaction hash or Ethereum transaction hash can be specified, with optional 0x prefix for the oasis paratime show command.

These both work:

oasis paratime show 2781982 985ab24c970a7901b864a89f26e54d14223e65d4edecca861cba8ec00becffc9 --network testnet
oasis paratime show 2781982 0 --network testnet

But, passing the 'Eth Hash' (0x4fcd824e3ca229b9703bf5887d70a99901268fe262bff1037929a1f4e708f860) doesn't work.

$ ./oasis paratime show 2781982 0x4fcd824e3ca229b9703bf5887d70a99901268fe262bff1037929a1f4e708f860 --network testnet 
Error: malformed tx hash: encoding/hex: invalid byte: U+0078 'x'

and

$ ./oasis paratime show 2781982 4fcd824e3ca229b9703bf5887d70a99901268fe262bff1037929a1f4e708f860 --network testnet 
...
Error: failed to find transaction with hash 4fcd824e3ca229b9703bf5887d70a99901268fe262bff1037929a1f4e708f860