UserCenterManager: Handle login errors caused by invalid credentials.
GiniSessionManagerAnonymous: Handle stored user credentials which are invalid.
Add test to GINISessionManager for checking the proper error when using wrong credentials
Increase JPG compression
Merge pull request #27 from gini/upload_improvements

Increase JPG compression
GINISessionManagerAnonymous: More tests.
Merge pull request #28 from gini/http_error_handling

Http error handling
GINIURLSession: Requests with an HTTP error code now resolve to an error.
Merge pull request #29 from gini/http_error_handling

GINIURLSession: Requests with an HTTP error code now resolve to an error...
APIManager: allow XML as response type (e.g. for getting the document layout)
GINIAPIManagerSpec: separate request checks for JSON and XML
Merge pull request #30 from gini/add_xml_response_type

APIManager: allow XML as response type (e.g. for getting the document la...
GINIDocument: add polling when requesting the document layout
Merge pull request #31 from gini/add_polling_when_requesting_Layout

GINIDocument: add polling when requesting the document layout
Merge pull request #32 from gini/XCode6

Updated dependencies in order to have XCode 6 compatibility.
Made class methods inheritable.
Use modern syntax.