[LMS-1211] added tooltips for entity type choosers

...client/web/client/application/model/DataSetTypeModel.java

...ent/web/client/application/model/ExperimentTypeModel.java

...lient/web/client/application/model/MaterialTypeModel.java

.../client/web/client/application/model/SampleTypeModel.java

...application/model/renderer/EntityTypeTooltipRenderer.java

...lient/application/ui/data/DataSetTypeSelectionWidget.java

...lication/ui/experiment/ExperimentTypeSelectionWidget.java

...t/application/ui/field/VocabularyTermSelectionWidget.java

.../application/ui/material/MaterialTypeSelectionWidget.java

...ient/application/ui/sample/SampleTypeSelectionWidget.java

.../generic/client/web/client/application/util/GWTUtils.java