Feature request: add account to use when --open

Those of us who regularly use multiple google accounts would, I think, greatly appreciate the ability to specify which account to be used for --open.

Example: I'm logged in (on the web side of things, in the browser) as both someuser@gmail.com and, using Google's multi-account functionality, someotheruser@corporate.com (which is still a google account, just connected to a corporate domain). The someuser@gmail.com account is my default.

Now, it doesn't matter if the project I'm working on is owned by someuser@gmail.com or by someotheruser@corporate.com – if I do a clasp --open then the browser will try to open the project as someuser@gmail.com.

I'd like the ability to do, for instance:

`clasp --open --account someotheruser@corporate.com`

Or something like that, anyways. Sorry if unclear.