EvolveAppTask.execute() now allows the caller to provide specific SQL

to execute (instead of the task-prepared SQL) and a list of evolutions

for signal emissions (instead of the task-prepared new_evolutions).
This will be used by some upcoming work to enable finer-grained batches

of evolutions and SQL statements that are calculated independently of

the task's full lists of evolutions and SQL.

Unit tests passed.
Tested this with in-progress changes that provide explicit SQL and

evolutions.