Add Spotbugs missing class and error reports.

[dlut_xz]

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

[dlut_xz]

Here is an example:

[Tomas Bjerre]

I would need the example in text format.

[dlut_xz]

spotbugs_result.txt