Make route width adjustable

[M4rtinK]

Requested by AL13N in Jolla Store comments.

The simplest way would be to just add a numeric entry field and let users set route width in absolute number pixels. On the other hand that does not seem like a very nice UX. Also there would be no feedback, so users would probably have to switch between options and the map multiple times.

So what about:

• adding a slider for setting multipliers/dividers for the default width (+ high DPI multiplier)
• adding a simple Rectangle based route width indicator
  • gray background rectangle
  • route simulation rectangle on top