DASCTEST-147 Specify plugin version that various plugins depend on, so
that if newer versions of the dependencies are added to the target
platform in the future, the older versions will be materialized.

Normally, the version depended on would be specified in the including
plugin. However, org.eclipse.emf.common.ui is only referenced via
package imports, so this is the only place we can specify the version.

This should be fixed up in master.