Redesign forms, display error messages

[bu-da]

From the feedback of the TA's:

• "The "Number of people" slider on the event creation behaves weirdly on my phone, it seems super sensitive in some ways (that's hard to describe maybe try on your side to see)"
• "When Selecting a picture, it is not totally clear if it would be from the gallery or the camera." => change icons maybe (folder and camera)?
• "When a new event is created, the view remains, which makes the user quesitons whether it was created or not."
• "Also the street, city and zip can be random values." => use the map instead maybe?
• "The participant slide shows two but is initialized to 0 so if untouched will not work."
• "The button in the creation of a recipe doesn't provide feedback in case of errors." => make sure to display errors in every form

Other issues:

• I can press done with an empty challenge form
• use map as well for events instead of address
• zero is also possible for events?
• no restriction of people for competitions, make it more alike events
• restrict to one image for tupperware
• use the official timepicker of android for competitions
• if you still have time may add a button to open a new chat to write sth to the host?