This PR adds questions that will be asked on railway and tram crossings.

The following questions are added:

• crossing:barrier=yes/no
• crossing:barrier=*
• crossing:light=yes/no
• crossing:whistle=yes/no
• tactile_paving=yes/no

The follwing questions are modified:

• crossing:bell

This is the schema after which I modeled the dependencies:

Currently still todo:

• Add pictures for the answer options for crossing:barrier=*-question
• Add explanatory pictures for crossing:light=yes/no-question
• Add a better picture for tactile_paving=yes/no-question(?)
• Add a picture of a "whistle-sign" from germany as explanatory picture for crossing:whistle=yes/no-question