EPlugin: separated out CamelStore getter from selected path getter
EPlugin: separated out CamelStore getter from selected path getter

* moved code which gets the CamelKolabIMAPXStore from
  the EShellView into a separate function
* use this new function inside the selected_path getter
  where the former code used to live in
* we will need this to enable the metadata / acl dialogs
  to retrieve the CamelKolabIMAPXStore so they can
  operate on the IMAP folders
* this will only work in the frontend, so the backends
  will need to cope with the server-side changes
  (for ACL, this is transparent, for ANNOTATEMORE we
  will need to involve the collection backend to remove
  the ESources for no-longer-matching folder types)

GNOME/evolution-kolab,GNOME/evolution-kolab