Allow dapp create to pass --value parameter

### What is wrong

I'm trying to deploy a contract with `dapp create MyContract` but want to deploy it with an initial ETH value. I tried passing `--value` but that doesn't seem to work for `dapp create`. My current workaround is to take the `seth send` command that is printed to the console, copy it and add the `--value` parameter to that as `seth send` understands the `--value` parameter.

### How to fix

It seems it would be natural if `dapp create` would allow the `--value` parameter directly.