New PollIntervalDialog and fix for infinite loop of pings when exception occurs

New dialog for asking for pull interval timeout with filter so only numbers can be inserted into the textfield.

Corrected problem with infinite loop when exception occurs when keepalive is started. There was no Thread.sleep() call in the last catch clause which caused hundreds/thousands ping requests per second.

Added dependency to oracle.db-api because without it JDeveloper 12.1.3.0.0 complains about missing file for class DBException.

Project files were automatically updated by JDeveloper to its new version so comitted them to the repo.