Introduce menu handling with one button

As introduction I've to write that I'm not really sure if we should add this complexity to the device. Besides the effort to implement this, the OBS should be easy to use and additional functionality always adds complexity for the user. At least we must do it as intuitive and usable as possible for a one button device. Looking at #28, #52, #53, #60, #86, likely others and the demand to switch between different presets stored on the OBS we seem to need such a functionality. Please share your thoughts.

Idea: Long press of the button (+1s?) is used as a different action than the current short press. If a long press occurs, the OBS goes to menu mode where you can cycle through menu items (short press) and select items with a long press. There can be a hierarchy of menus, 1st item is always < back (do we internationalize this?), there must not be more than 5(?) items on one level. Likely all functions will be paused while in menu mode.

The 1 char of the item shows the action < is back, > leads to a sub menu, * triggers a direct action, ? triggers an action after a additional confirmation.

Main

< back
? delete last
* mark private
> pause recording
> select preset
> info
> system

Main - delete last

Delete last overtaking
* yes
* no

Main - pause recording

Paused
< back

Main - select preset

< back
* Bike 1/Art3mis
* Bike 1/Parzival
* Bike 2

The preset contains things like the left and right offset, user id, ...

Main - info

< back
* version: v0.3.444
* 30 cm left offset
* 30 cm right offset
* 454 reports
* 5 sats
* 12:00 2020-11-24
* 3.2 V
* ...
* filesize: ???
* ....

(all actions go back to the active mode)

Main - system

< back
? restart to server
? restart
? halt
* demo
? erase

Start by reviewing issues #28, #52, #53, #60, and #86 to understand the existing demands for menus and preset switching. Then inspect the firmware's button-handling and device-mode entry points, which are not named in this issue. Done would require an agreed menu interaction design and a defined implementation scope for the one-button device.