adding ghapi::EMail
some code cleanup
add a general HTTP GET method for Manager

Some queries will not be directly on a Thing
add handling for retrieval of all EMails to User

todo: add check, whether the current user is actually the authenticated
      user
removing some debug output
add test case for User::getAllEmails()
add checks for User on authentication and correct scope
enabled conditional requests for generic Manager::get
enable conditional request for all user's emails
some code cleanup
add base URL of GitHub API as global variable
made API_BASE a QUrl for more convenient handling
add API endpoints for authenticated user and authorizations
use new defined API endpoints
Merge branch 'global-api-base-url' into add-emails
moved API endpoint definitions to separate header
using API endpoint definition for /user/emails
fix compiler warning (insecure format string)
Merge branch 'add-emails'