Ignore test-generated artifact
Remove obsolete length parameter from step insert/remove cache signals

The length parameter is incorrect under many circumstances, and has
proven so difficult to get correct that the cache implementation now
ignores it entirely. Remove this tech debt to simplify future ops.
Eliminate unnecessary conversion from cursor steps to range
Remove unnecessary (and impossible to use) constraint argument

The constraint function only allows a choice between two adjacent steps
if the supplied position is not exactly on a step. With things such as
inline roots and other complex features of the addressing system, this
is extremely difficult to use correctly.

As it is currently unused, the best thing to prevent future problems it
to terminate it now!
Remove unnecessary test returns (again!)

These were just cleaned up, and here someone has gone and reintroduced
them again! What gives!
Merge pull request #600 from peitschie/cleanup

Remove sharp edges from various APIs
Fix property removedProperties of ops.OdtDocument.signalMetadataUpdated

was passed as removedProperties.attributes: !string
instead of    removedProperties: !Array.<!string>

also
* reuse initial spec variable
* only deep clone opspec.setProperties, as removedProperties is cloned by
  opspec.removedProperties.attributes.split(',') already
Init removedPropertiesArray to null, is understood by OdfContainer.setMetadata
Add gui.MetadataController