Task-number: BAUHAUS-447
Task-number: BAUHAUS-639

overshoot is deprecated

Reviewed-by: Thomas Hartmann

- also removed tabs from Qml files

- clearing search input focus when clicking clear icon
- re-set updated sections' models
- using GridView-based item selection
- C++ code cleanup
- Manhattan-length used for drag & drop initiation
- integrated QtCreator's filter text input
- replaced QToolButtons with a QTabBar
- fix: eliding text & corrected selector offset
- styled resources view
- updated Qml syntax

Reviewed-by: Christian Kamm

- view is not moving anymore when opening/closing sections

among others, the scrollbars of the Items and Resources views
have the same size and position now

Task-number: BAUHAUS-204
Task-number: BAUHAUS-207
Task-number: BAUHAUS-339
Task-number: BAUHAUS-365
Task-number: BAUHAUS-374
Reviewed-by: kkoehne