Finish basic create call to work with real appway

 - add app.name param
 - add app.manifest param
 - add Request#http_options
 - add example manifest file for github.com/threez/appway-example
 - stub out request for api spec
Replace Api#method_missing with #request
Refactor whole Api implementation

 - only mock classes heavily depending on external implementation in api specs (endpoints + http)
 - extract Xway::Api::Request::Body class
 - add debug flag to Http class
 -