Improve pip plugin options support

* -r, --record now looks for a local file instead of trying to cache
  the entire package index
* add --editable because it's useful
* add --single-version-externally-managed because it is too long
* add --record and --root because they're required by
  --single-version-externally-managed
Merge pull request #2043 from quodlibetor/fix-pip

Improve pip plugin options support