Expose the hosts provider and support ssl in client

[ssalinas]

• allows the user to more easily set a Provider<List<String>> for hosts in the BaragonClientProvider (this was possible in the constructor before, but not the provider). Does the same for auth key
• hosts are now http(s)://host:port instead of just host:port so that we can easily support ssl. Values will be prepended with http:// if only the hostname is passed in (not checked for the provider, only for the static list of hosts)
• A 404 for a collection now throws a BaragonClientException with a status code of 404 instead of returning an empty list

@jhaber

[ssalinas]

Further tweaks, updated this so the client can just take in full base urls instead of having to always specify contextPath separately