Follow links to directories when activated

We may find a link that points to a directory. Activating the row with
the link should show the directory that the link points at. Resolve the
link and show any directory that the link points to.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Refactor directory selection to separate method

We're switching current directory at various places. This could be prone
to errors since a change would have to be made at all of them.
Consolidate the code that switches current directory to a separate
method that they can all call.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>