[cli] dapp build

[florianlenz]

Feature

The pangea cli should be able to build a DApp to an installable bundle.
The command (dapp:build) should take a singing key file as it's first params and --dev as an flag.
By default we build for production. The build is signed with the given signing key.

Acceptance criteria

• build the project (@hunght)
• sign the build (@florian)