Allow compatibility with demandlib v0.2.2

Compatibility with demandlibhas been in the works for quite a while, and now lpagg 0.19.0 is compatible with demandlib 0.2.2.
It is an alternative source of load profiles, compared to the built-in sources in lpagg. If the configuration yaml file includes the following, demandlib is selected as a source.

settings:
  use_demandlib: True

In that case, the demandlib implementation of VDI4655 is used for residential buildings, and the BDEW profiles from demandlib are used for commercial buildings, each providing space heating, domestic hot water and electricity profiles.

While those sources have their own APIs in demandlib, lpagg provides a unified workflow to generate all those profiles from a single input set of buildings. lpagg also handles daylight saving time, simultaneity effects and allows the use of custom weather data, while trying to be memory-efficient when non-unique profiles would be generated for thousands of buildings with overlapping settings.

Full Changelog: 0.18.4...0.19.0