#669 Cutting on stack call

The class Packages represents the packages that must be filtered when the stacktrace will be printed, an instance of packages are passed to the Tracefilter, that do the filtering....

- If the user pass -filterstack argument, the stack will be filtered with some "default packages".
- If they pass -filterstack [pkg1, pkg2, pkg3], the pkg1, pkg2, pkg3 will be filtered from the trace (-filterstack [java.lang, junit.framework, ...]