auto-indent: only format params if more than 1

No sense in formatting parmameters that are just a single item.
Easier to just leave it be since they will never match up with the
surrounding functions in a header anyway.
commands: move workspace and active tab to GbCommandProvider

This refactors the workspace and active-tab properties into the
base class, GbCommandProvider. They are likely to be needed by
most providers, so might as well track things there.
commands: add a vim command provider

This adds a provider that will check to see if the command is a VIM
command and then dispatch it to the GbEditorVim of the active tab.

It should only complete if vim-mode is enabled.