Allow optional named adapter for intranet portlets

[Tres Seaver]

Currently, the intranet allows only one portlet view for any
given item.

Update the code which parses the list of portlet paths to allow
an optional adapter name. E.g.:

  /path/to/item
  /path/to/item foo

would create two portlets, one using the default / unnamed
adapter, and the other using the adapter registered with name
'foo'.

For motivation, see:

https://github.com/karlproject/karldocs/blob/master/docs/specs/drafts/public-blogposts-portlet.rst

[Tres Seaver (tseaver)]

Work in the 'karl' package will be on the branch, 'tseaver-1150171-named_portlets'.

[Tres Seaver (tseaver)]

KARL changes pushed to that branch.

[Tres Seaver (tseaver)]

On branch 'tseaver-1150171-named_portlets', pushed to multikarl w/ branch 'm125-multikarl-test'.