frontend: range input widgets should support manual value entry

[ES-Alexander]

Current behaviour

You have to physically move the widget to the desired value, even if you know exactly what value you want it to be. If the widget covers a significant range then precise values are difficult and time consuming to achieve, so manual entry can be preferable.

Expected or desired behaviour

1. Add a "Show Value" option to sliders
   • This could be with a radio button of Show Value: ( tooltip | entry | off ), since some people would want neither, but it seems unlikely someone would want both at the same time
2. Make the value entry for both sliders and dials editable, instead of read only

Prerequisites

• I have checked to make sure that a similar request has not already been filed or fixed.