fix(GroupAccount): Implement clear() method to correctly flush/empty group's content (refs #4541)
test(GroupAccount): Add test for GroupAccount::Clear() (refs #4541)
test(Dir): Add test for Dir::Clear() (refs #4541)
Merge pull request #1101 from eguaj/3.3-A4541

fix(GroupAccount): Implement clear() method to correctly flush/empty group's content (closes #4541)