* Use id() for methods returning a string used to represent
    some type of object.
  * Use displayName() for strings that are meant to be user
    visible.
  * Quieten some warnings while touching the files anyway.
  * Move Factories to their products in the plugins where that
    was not done before.

Reviewed-by: dt

 * Make sure all non-empty source files found below ./src have
   a copyright header.

Reviewed-by: con

Reviewed-by: Daniel Molkentin
Reviewed-by: Friedemann Kleint

Added IExternalEditor which knows a kind and a mimetype.
Make EditorManager and ProjectExplorer "Open With" query
the interface and add the respective kinds.
Add "openExternalEditor" to EditorManager.
Add External editors for Designer and Linguist,
making use of Mac 'open' or Designer's Tcp socket mechanism
to ensure files are opened in the same instance (per Qt version).

Task-number: 249392
Reviewed-by: con <qtc-committer@nokia.com>