Describe current fill erase behavior
Summary: Adapt class description for fill / erase tools
Test Plan: read the class description
Reviewers: kislinsk, O1 MITK Reviewer Group I
Reviewed By: kislinsk, O1 MITK Reviewer Group I
Subscribers: kalali, kislinsk
Maniphest Tasks: T29132
Differential Revision: https://phabricator.mitk.org/D629