[UX] Save data client side while user is on walk

[robertfausk]

and persist data server side when walk is finished and user got internet connection.

• maybe in combination with PWA
• e.g. https://developer.mozilla.org/de/docs/IndexedDB

Workflow could be something like:

• Given user is authenticated (needs connection once but only for login)
• user starts a walk (needs no connection; client side saved)
• user goes from way point to way point and finish its walk (needs no connection; client side saved)
• automatically or manually persist walk after finish server side if connection availably
  ** otherwise show badge in menu (or something else that there is data that needs to be saved)
  ** this badge is an info badge (if manually triggered action by user needed)

Attention:

• Give user Feedback about persisting and non persisting otherwise he could be confused when he looks up in backend and there is no walk.
• Two users will not be able to write in same walk.