Keyboard shortcuts for providing answer options on Find projects

[ofr1tz]

Is your feature request related to a problem? Please describe.
Users are currently able to use keyboard shortcuts (number keys) to provide answers to projects of type Validate and Compare. In Find projects, however, only navigation shortcuts are currently available. Full keyboard accessibility without the need for mouse interaction can improve contribution speed and user experience for some users.

Describe the solution you'd like
The solution would need to different types of keyboard interactions:

1. Select/cycle through the image tiles that are available on the current page
2. Provide an answer option for the selected image tile (by number keys, for consistency with other project types)

Additional context
Refers #9

[slautenb]

Would be a really nice feature. Would also be nice to find the shortcuts in the tutorial section.