Kill MCollective submodule and add externalsources directory to .gitignore

The idea here being that this and the puppetdb repo will be managed by the rake toolchain.
Blow away our copy of the puppetdb 1.1 manual

For great de-duplication.
Better data format for external sources in _config.yml

No need for multiple root-level keys -- each source can know what its
real upstream repo is, and we'll just handle de-duplication later.
First try at this new way of managing external docs -- see below for caveats

- Requires git-new-workdir be installed in the $PATH, which we'll have
  to change because it doesn't ship w/ git-core.
- No idea how it handles network failures.
- But it works!
Silence task descriptions of some non-user-facing tasks to chop down the list of tasks