Add custom graph to the list of available project activity graphs

These graph must allow to:

• select metrics:
  • up to 3 metric per graph
  • max 4 graphs
  • 1 graph can only have metrics of the same type
• be used to directly display the evolution of a given metric when coming from:
  • the "trend" icons of the project home page (see SONAR-8611)
  • the Measures page => we should replace the "history" charts by a similar "trend" icon that also points to this graph