Add Base URL parameter to AOSmithAPIClient Constructor

[AlanLivingston]

Hi Brandon,

I noticed AO Smith changed the server again so that r2.wh8.co returns LOW, MEDIUM, HIGH for water status, and r1.wh8.com returns the numerical values. I saw that you changed py-aosmith to parse the hot water status as they change servers.

I've implemented a change that takes a base URL parameter in the AOSmithAPIClient constructor allowing users of py-aosmith to specify the server to use, and uses API_BASE_URL if nothing is specified. My motivation is to allow the server change in HAOS using a setting in configuration.yaml, but I don't have that working yet.

Let me know if you think this is worthwhile pursuing.