This PR ensures that all 3 ways of handling key events are wrapped with exception handling logic, so that user exceptions do not cause unstable states and are correctly reported.

* Added a generic tooltip widget

* added the header

* finished dropdown widget

* removed mock state

* Added step 1 substeps

* stepper tests fail

* tests still fail

* removed redundant checkbox

* removed test data

* full fixes based on Chris' comments

* changed widget's name

* changed statefulwidget, added test

* fixes based on Casey's comments

* empty commit to kick pending checks