Tracing tool: inherit basic actions from Navigator

... instead of defining them all over again.

This commit removes the navigation actions (zoom, pan) from the
Tracing tool and instead gets them from Navigator.

It also removes a keycode ambiguity between '.' and 'DEL'. Moving
down in z now only works with the actual '.' key and not with the one
on the numeric keypad. Before, in Navigator, one could also move down
in z with the 'DEL/.' key on the numeric keypad. However, this key is
used to delete the active node in the Tracing tool.
Tests: fix project and stack insertion tests
Tests: fix authentication test
Tests: assign new test user required permissions

The test user must be able to browse and annotate in this test case.
Text labels: unify parameter names and table column names

This gets rid of some odd special cases and also lets one more test pass.
Don't repeat error message when root node can't be deleted
Include success message when treenode is removed
Use better error type when neuron/skeleton retrieval fails

A ValueError is more descriptive than Exception.
Tests: let index test work with current API
Tests: remove some artifacts referring to the object tree
Tests: update expected messages to current API
Tests: replace deprecated mimetype with content_type in response objects
Tests: fix basic label tests
Tests: add FIXME for driver lines test case
Tests: remove debug output
Tests: use predefined user in common API tests
Cancel connector retrieval early when there are no connectors
Don't require stack ID for retrieving connectors
Connector table: remove code in comments
Tests: fix connector tests