Class ProgressPart disposes system cursors

This causes https://issues.jboss.org/browse/JBDS-2503
Only Add Custom Capabilities wizard creates progress monitor based on this class, so that the issue can be reproduced only by adding custom capabilities as described in JBDS-2503.
After wizard completes, it is impossible to work in Eclipse, because system wait cursor is disposed, and almost all jobs in Eclipse invoke that cursor.