New option for climate device to expose temperture sensors

[spacegaier]

Description

Add support for exposing the current and target temperature as sensors from a climate device.

In regards to the sensor naming: The weather device uses underscores to add the suffix, but in HA that looks bad, so I instead went with spaces. Ideally we would use one approach consistently in the library.

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have performed a self-review of my own code
• The documentation has been adjusted accordingly
• The changes generate no new warnings
• Tests have been added that prove the fix is effective or that the feature works
• The changes are documented in the changelog
• The Homeassistant plugin has been adjusted in case of new config options

[farmio]

LGTM.
Only thing to consider is renaming "expose_temperature_sensors" to eg. "create_temperature_sensors".

[coveralls]

Coverage increased (+0.006%) to 94.912% when pulling 2c4cce1 on spacegaier:climate-expose-temps into 7521754 on XKNX:master.