Save entity configuration in a file, so we can run it automatically

These modifications allow to save entities data after the creation of an entity in a .jhip file. 
This file can be loaded instead of manually typing all the information of an entity:
   yo jhipster:entity nameOfEntity.jhip
 It is useful when you make mistakes at the creation of a project. You can restart the creation and easily load good entities from files and create again the wrong ones.