Add a vector layer to printpreview example.
Disable tileManager for maps in PrintMap panels.

Also set the same defaults for new maps as in the Map panel.
When cloning: no need for special handling.

Previously Vector layers wouldn't be cloned, but recreated from scratch
and would e.g. loose styling from StyleMaps. See #217.
Whitespace cleanup.
Merge pull request #224 from marcjansen/printpreview-vector-example

Fix several issues in the `panel.PrintMap`-class (r=@bartvde)