feat(ecg-app): Refactor ECG App

New Button-Layout
=================

          /-----------------------\
          |   xxxxxxxxxxxxxxxxx   |
          |                       |
          |                      <> * Pause screen
          |         card10        |
 +------- <>                     <> * During pause: Scroll right.
 |        |                       | * Short press: Toggle between Finger
 |        \-----------------------/    and USB.
* During pause: Scroll left.        * Long press: Toggle bias on/off.
* Short press: Toggle LED mode.
* Long press: Start/stop logging.

Other Changes
=============
- Split the bar into negativ [10:5] and positive [5:0] scale and update
  them seperate to have a better visualization.
- Blink red with backside LEDs on detected pulse.
- Allow toggling the LED modes on and off (see new button layout).
- Lock mode & bias during logging.