Add display time format option hh:mm

[afreisinger]

Fixes #136

• This PR is compliant with the other contributing guidelines as well (if not, please describe why).
• I have thoroughly tested my contribution.
• Should this code require changes to documentation I will contribute those to https://github.com/ThingPulse/docs.

• Add time format option hh:mm on display
• The settings.h file was modified to be able to choose the visualization.