Provide Pub console

[jonas-jonas]

When synchronizing a project's dependencies, pub outputs any errors as well as standard output indicating what changed.
We should show this in a dedicated console.

Tasks:

• Pub console (showing standard & error output)
• Option in settings on verbosity [all, error, io, normal, solver and warning]

I tried it already with a launch configuration, but that seems to not allow to also use a job with our current structure of displaying what's happening in the Progress view. An alternative is to follow https://github.com/eclipse/buildship approach on this and roll our own IOConsole implementation.

[lak-proddev]

@jonas-jonas If I am not wrong, we already have a solution right? #93

It will show like this.

[jonas-jonas]

See my comments on #121