Update bwtester dials

[mwfarb]

A number of requests for the bwtester dials exist that need a different library to handle, since the jQuery Knob library currently may not be well-suited for them (https://github.com/perrig/scionlab/pull/37). This will enumerate those requests for another PR.

• Dials should show min and max value numbers.
• Dials should show hash marks for interim values.
• It's useful to edit the actual number value, but it should be styled closer to user expectations for an input field.
• Particularly, the bandwidth dial should show a color range from green to red.

[mwfarb]

As noted in #44, the dials have some unexpected behavior that should be remedied as well:

• The delete key does not work in the input field
• left/right arrow keys decrease/increase the values instead of navigating the input