Add optional step argument for slider, etc.

[utopicchaotica]

Is your feature request related to a problem? Please describe.
For some number inputs, it's more user-friendly to have steps (number intervals) instead of just increasing/decreasing by 1, e.g. it makes more sense when you're dividing a cookie recipe that originally makes 12 by 2, 4, or 6.

Describe the solution you'd like
Be able to add steps(#) as an input argument. Looks like it's already in the generated HTML as step="1"

Additional context
N/A

[mProjectsCode]

TODO: add the step size to the progress bar as well

[mProjectsCode]

released as part of 0.7.0