Avoid change directly after loading.

Setting the _selected field on a model causes a navModel update, which in turn
causes head to change because of serialisation differences. To avoid this, we
don't call setNavModel if only _selected has been changed.

One other small change to avoid doNotReparse from leaking out.
Fix parsing of metadata in opf file.

Data should not be persisted inside `parse`. Instead the result
should be returned so backbone can persist it with the correct
options applied.
Merge remote-tracking branch 'origin/master' into avoid-saving-nav-on-load
Merge pull request #172 from oerpub/avoid-saving-nav-on-load

Avoid change directly after loading.