Improve recrutement pattern of ai

[rodolphecombe]

Optional :
Make ai stop recruiting when income becomes negative (recruit event) and start recruiting again when it becomes positive again (die event).
Make it a macro with leader id and maybe side to add at scenario level.

[rodolphecombe]

Income must be set to support half the units that should be recruited and gold must be cut by half.

[rodolphecombe]

First tests show that giving high gold plus high income does not work.
Now testing default gold and high income.

[rodolphecombe]

Implemented in 0262865
Tested in scenario 10, to be tested in the others.
To merge after for 1.18 version after tests.