[conso] Changes in allocation not taken into account

[slipsl]

Changes made to an existing allocation should appear in the conso DB.

For example:

• Project rgzi / idris: the allocation went up from 40,000 to 60,000 hours on July 2nd 2016;
• Project gencmip6 / tgcc: the allocation went down from 75,000,000 to 60,000,000 hours on July 26th 2016.

To keep track of the evolution, a new line could be inserted in the conso.allocation table with the new value and start_date = the date on which the change occurred, and the existing line could be updated (end_date = the day before the change).

[SebastienDenvil]

it was decided today during the platform meeting to have this in priority 2.

Later we will need the consumer to detect if the allocation changed compared to the latest insertion and to insert the new one once when necessary.