Proposal: splitting pub and flutter

[jack-r-warren]

In working on #166 it became apparent to me that there's a number of cases where you'd want to run a command on all of the Flutter or non-Flutter packages. I can also imagine a number of other dependency-related tasks like #117. The following would be a breaking change but would allow room to grow:

• mono_repo pub: argument pass-through to pub executable, run on all non-flutter packages
• mono_repo flutter: argument pass-through to flutter executable, run on all flutter packages
• mono_repo dependency (abbreviation dep?)
  • get: do pub get or flutter packages get across all packages as needed
  • upgrade: same for upgrade
  • override [add|remove]: add or remove sibling overrides (Allows population of dependency_overrides #117)

The change would be breaking for anyone currently using mono_repo pub [get|upgrade] to work with Flutter dependencies. It might make sense paired with #145 in a major version bump.

[kevmoo]

Closing as duplicate of #45