[LMS-590] minor change: introduce constants

...eneric/client/web/client/application/ui/ColumnFilter.java

.../generic/client/web/client/application/ui/GroupModel.java

...eric/client/web/client/application/ui/amc/GroupsView.java

...ric/client/web/client/application/ui/amc/PersonModel.java

...ric/client/web/client/application/ui/amc/PersonsView.java

...neric/client/web/client/application/ui/amc/RoleModel.java

...neric/client/web/client/application/ui/amc/RolesView.java

...t/application/ui/sample_browser/GroupSelectionWidget.java

...client/application/ui/sample_browser/SampleTypeModel.java

...lication/ui/sample_browser/SampleTypeSelectionWidget.java

...eric/client/web/client/application/ui/amc/CheckGroup.java