Add temperature and humidity sensor

[afreisinger]

Fixes #134

• [x] This PR is compliant with the other contributing guidelines as well (if not, please describe why).

• [x] I have thoroughly tested my contribution.

• [x] Should this code require changes to documentation I will contribute those to https://github.com/ThingPulse/docs.

• Add optional temperature and humidity sensor

• Add screens and icons.

• Modified settings.h with GPIO and TYPE SENSOR and IS_PRESENT conditional.

[marcelstoer]

@squix78 WDYT?

[marcelstoer]

Again, thanks for your contributions.

For this to stand a chance getting included I see a number of necessary changes:

• interaction with a sensor has to be abstracted through a coding interface or at least something like it supporting compile-time linkage
• all of the DHT specific code, including it's inclusion of a specific driver, has to go into a dht.h or even dht22.h
• if someone wants to support a different sensor they would need a <my-sensor-type.h>, it will contain all the same (public) function signatures as the dht.h
• in the settings.h or the .ino you would then include your specific sensor header file
• the processing code in the .ino will have no idea whether it's talking to a DHT22 or something else as will only call something like sensor.getTemperature()

[afreisinger]

Nothing to thank for. I will shuffle and give again !