Test to enable drop down selections for RDFauthor

This is a test to enable dropdown selections for the RDFauthor. The new
dropdown widget is a modification of the literal widget which needs to be
customized further. There is also only minimal error handling right now.

Usage: If a (datatype) predicate has an rdfs:range A and A has an owl:oneOf,
the dropdown widget will be used, i.e. in this situation:

    :predicate a owl:DatatypeProperty .
    :predicate rdfs:range :dropDownExample .
    :dropDownExample owl:oneOf [ "Ex1"^^xsd:string, "Ex2"^^xsd:string ] .
Fixing obvious mistake
copyWithObject will respect a passed type

When editing with RDFauthor, there is a method called
copyWithObject that copies a statement's subject and predicate, but
exchanges the old object for a new one. However, there is a line of code
that explictly adds the type of the old object to the new object.
We now check first if the new object has a type and only add the old type
if no type is given.
Dropdown will now also support resources (uris)

The dropdown selection will also support resources with labels and display
a label in the dropdown selection, but write an uri to the triplestore.
This is still work in progress and will probably still be buggy. Also
updating requires a reload.
Fix a bug in rdfauthor.statement.js

This commit fixes a bug that was introduced with commit
d5f6dabbd276f8f1f58cc7bc2ceadc1b445b3c38
Fix: Full URIs in rel/property attributes

Full URIs in rel or property attributes are not parsed correcly. The
'http' is treated as namespace prefix.
Fix: Pass options to subsequent new widgets

When the plus button next to a widget (or 'input field' in GUI terms) is hit,
a new widget will be inserted. Options from the first widget will now be
passed on to this new widgets. This is especially needed for the new
dropdown widget.
Reset without reload

Dropdown widgets don't require a reload of the page

Note: Reset for dropdowns with literals is a TODO.
Feedback when submitting values

This commit works towards a better feedback when submitting values
without reloading the whole page.
Merge branch 'feature/rdfauthor-FormBuilder-dropDownTest' into feature/rdfauthor-FormBuilder
Set default max dropdown size to 6

Queries for dropdown values are very slow in OW, although they are fast with
Virtuoso. Some optimization is needed here. As for now, we restrict the
max number of dropdown values to 6.
Some more unification for update without reload

Widgets literal, resource, datetime and dropdown now will all reset the
page without reloading and give a unified feedback via the new
rdfauthor.tools.js