feat(ecg-app): settings menu [MANUAL MERGE]

• settings menu based on simple_menu to set options instead of overloading buttons several times:
  • new option: length of plotted time window
  • new option: log pulse instead of (or additionally to) the full ecg graph
  • new option: sampling rate
• store the settings to persist to next launch
• some cleanup that is desperately needed in this app
  • create folder for output files
  • rename 'histogram' to 'graph' as it is not a histogram
  • approximate timestamp (and cache log filename) to reduce number of time intensive system calls on pulse logging