Adjust error message raised when a git repo could not be created
Add a default configuration for the folder containing the git repo for the tickets
Add a ticketfolder argument to the new_project method of the internal library

This ticketfolder variable contains the name of the folder that will
contain all the git repositories for the tickets
Adjust the new_project method in app to set the ticketfolder configured for the application
Adjust the README so that the default `tickets` folder is created
Add method to the internal library to convert a ticket into JSON