Enable decimal time display

Optionally: Support decimal time in the time selection dialog

Caution: be careful when configuring "regular time" (base 60 minutes) with "decimal total" (base 100 minutes):

• Regular (base 60) minutes can have rounding deviation when converting to decimal (base 100) minutes.

• Sample: 00:20 (20 minutes) is equivalent to 33.3333 decimal minutes, which the app shows as "00.33".

• However, three work units at 20 minutes summarise to exactly one hour, i.e. the app needs to show "1.00" in that case (instead of "0.99").