Issue #1 Improve performance for large java file (and large code bases) …

Added more diagnostics for refactorings + a debug mode:
- whether refactorings are faulty when they throw an exception
- whether refactorings are badly behaved by telling they made refactorings but actually did not contribute any
- in case of infinite loops, report possible culprit refactorings.

AggregateASTVisitor.java:
Added a ctor with a signle IRefactoring for unit tests.
Added continueVisiting(), getVisitorsContributingRefactoring(), logBadlyBehavedVisitor(),

AutoRefactorHandler.java:
In applyRefactoring(), in case of infinite loop, reported possible culprit visitors.
Added getPossibleCulprits().
Fixed hyperlinks in javadocs.

PreferenceConstants.java, PreferenceHelper.java, WorkspacePreferencePage.java:
Added a "debug mode on" preference.