fix(ResourceRoute): returns NULL if constructed URL is NULL
fix(ResourceRute): construct url for action dictionary
fix(XmlMapper): reset document content in evenry call 

resolves #31
fix(ResponseFactory): remove DataUrl mapper from response factory

DataUrlMapper is not compilant with mappers API since it requires
object of type Media. Therefore any request with Accept header
appliaction/x-data-url results in server error.

resolves #17
refactor(InputFactory): use Nette getRawBody if available

resolves #32