unify identification handling

Javascript and php now both use `identifier` for variables that
contains relevant information to identify the elements.

Naming guideline:
- `elementID`: The id that is saved in the database and identify an
existing element
- `identifier`: Unique identification for elements when adding/editing
a page. This may be the elementID stored in the database for already
existing elements but also can be temporary ids to identify an element
across several requests
minor page element save improvement
element update code
adapt changes to news element type
Merge branch 'master' into search