Added TopPerformers API result sample
Added top performers URI
Moved result models to dedicated namespace
Added model and sub-models for TopPerformers API.
Factorized the localizable result (classes containing a countrycode and a resource dictionary).
Fixed TopPerformers Uri (from base/TopPerformers to rankings/TopPerformers)
updated GetResult and URI builder to handle null / no query parameters.
CSProj for new models.
UnitTests for TopPerformers API
Merge branch 'feature/Top_Performers' into develop