FR: add a stop watch + reset stopwatch buton

#### Problem description
In some case people need to count a frequency, having a stopwatch available in addition to the counter will enable such action without too much constraint for the user

The stop watch could be activate be the intent params

The stopwatch and the stopwatch reset button could be under the counter buttons in a single line

No files or tests are named. Start by locating the counter screen and its intent-parameter handling in the Android app, then verify how the existing counter buttons are laid out. Done means an optionally activated stopwatch and a reset button appear beneath the counter controls and reset the stopwatch as described.

Written by the indexing model from the issue text.