Add Spotbugs missing class and error reports.

[fcgxz2003]

FindbugsParser.ParseReportOutput methods can only parse bugInstance of spotbugs.xml, but spotbugs can give missing class and error reports.
So add ParseMissingClassReportOutput and ParseErrorClassReportOutput.

[fcgxz2003]

Here is an example:

[tomasbjerre]

I would need the example in text format.

[fcgxz2003]

spotbugs_result.txt