…redicate functions so identical logic can be checked in the condition_variable wait function and also inside the election_scheduler processing loop. This allows new predicates to be easily added and also eliminates risk of disjoin checks between the loop and the condition variable.

…scheduler::manual since the semantics of ::manual will be changed to not wait for vacancy before inserting.

… vacancy is not considered and elections are started for any blocks passed in.

- Moves responsibility for trimming down election count from active_transaction in to election_scheduler. This is done so that more advanced filling/spilling can be done by the election scheduler in the future.
- Erases from the active_transactions container by oldest transaction rather than by newest.

… vacancy is not considered and elections are started for any blocks passed in.

- Moves responsibility for trimming down election count from active_transaction in to election_scheduler. This is done so that more advanced filling/spilling can be done by the election scheduler in the future.
- Erases from the active_transactions container by oldest transaction rather than by newest.

…entry points to .erase in future