Load less data / use synthesis when possible

We could make a better use of the synthesis to:

• load only the synthesis of all GHGIs when entering the application (currently we load all the data of all GHGI)
• load only the synthesis when displaying the public page (same as above)
• ...

This will probably required to introduce a true GHGISynthesis object client side (and not mix it with the current GHGI object)