enable split-time activation modes - continuous, manual, auto, semi-auto

[tshalif]

split time measuring should have the following modes:

1. continueous
   ROWING_START event is fired as soon as entering this mode, ROWING_STOP is never fired. Long press on time meter will reset avg/count split time/distance meters
2. auto
   rowing starts/stops automatically based on rowing detection
3. semi auto
   same as auto, but start-enabling triggering event must be received in order for auto start to perform
4. manual
   start/stop manually

In addition, there are the following non-mode options:

• reset meters on start
  zero meters when starting - either manually or automatically

manual zero/reset by long press should also be possible at any time