refactored buildQuerString method, it now accepts two arrays as params and returnd querystring
specify requiredUrlParams on providers config as a array of strings instead of an object
concatenate passed urlParams with default urLParams
use requiredUrlParams directly from the object instead of passing to buildQueryString()
added helper camelCase function to convert param names from from underscore to camelcase
set redirectUri on facebook provider as part of default config