Remove smart pickers

[julien-nc]

Because they are included in the Assistant app now.

• [x] Remove smart pickers
• [x] Remove reference widgets
• [x] Remove unused npm dependencies
• [x] Remove useless DB tables
• [x] Delete DB migration steps that add tables that were removed
• [x] Adjust README and info.xml
• [x] Adjust tests
• [x] Bump app version to 2.0.0

[marcelklehr]

Bump app version to 2.0.0

:blue_heart: