Move data validaton and marshalling into `Home` factory method

[RobertoRoos]

As the title suggests - parser.py is currently not very DRY, most parsers repeat the same kind of validation and marshaling rules. It could be cool to move this to something more central.

[RobertoRoos]

This was coincidentally discussed in this excellent comment by @wtfloris : #128 (comment)

I'm responding to that specific comment here:

You have a good point.

• I would keep all parsing to the specific parse methods then.
  So e.g. a specific parser will know that the city name is embedded in res['_result'][0]['city']['name'] , or to scour the HTML.
  Indeed, it wouldn't make much sense to centralize this because the origins of the data are all different.
• But I would still insist on moving all validation and patching to something central.
  Things like "a city name is required" or turn "€1'234.99 into 1234" will always be the same across all parsers.
  You mention the "Appartement" prefix for Pararius, I see no harm in always removing this prefix, because where else should we want to keep it?

I made a quick draft, see #130 for what it might look like.