Allow next/back to be triggered by right/left arrow keys (and/or tab)

[yeah]

It would be helpful for people who are more keyboard-focused and/or especially in tours that explain form fields.

Here, it would also be great if the tour would follow the current focus. This way, one could "tab" through form fields and the tour would always explain what can be entered in the current field.

[yeah]

Depending on how much time is left on our current project, we may get around to implement this ourselves and would submit a pull req.

[ermauliks]

+1.

Edit:
Workaround: #8

[timlindvall]

Rolling this issue into #103.