Added test-output directory to .gitignore.
Removed never used imports.
Used foreach loops.
Removed unnecessary casts.
Fixed several issues:

LaunchUtil.java:
When running a test method, changed the launch name to use the
simple name of the  test class (just like when running a test class).

ConfigurationHelper.java:
When running a test method, just run that test method
instead of the whole class.
When running a class, run the  whole class, not just the method
referenced in the test.

SuiteRunInfo.java:
Enabled the "Run last failed" button: m_suiteCount is a bit out of
whack. Changed the condition to enable the button.

TestRunnerViewPart.java:
Prevented a NPE in getLastLaunch().
Calling code is already protected against NPE.

TestNGMainTab.java, TestNGLaunchConfiguration.java:
Further fixes for running test methods.

QuickRunAction.java:
Avoid NPE in run().