Fix handling of the custom protocol on windows

[MarshallOfSound]

Fixes #271

[MarshallOfSound]

This allows the defaultProtocolClient to work from npm start (so you don't need to be packaged for it to work). It also makes the alert appear on windows by handling the argv parameter in the makeSingleInstance callback

[zeke]

@MarshallOfSound if electron/electron#8052 lands, would it render this PR unnecessary?

[MarshallOfSound]

Yep

[MarshallOfSound]

@zeke Actually a subsection of this PR is still required to make the protocol handler work from a non-packaged version of the app

[zeke]

Just checking in here. @MarshallOfSound is this still something you want to ship eventually?

[MarshallOfSound]

Yeah, the PR in Electron needs to ship first though

[ckerr]

@MarshallOfSound are this and electron/electron#8052 still something that you want to land? If so, is there anything I can do to help unblock these two?

[ckerr]

@MarshallOfSound ping :D

[codebytere]

oh wait i lied, the other one landed so this is unnecessary

[codebytere]

Closing in favor of updated one.