Add sourceSave() and sourceDelete() methods notifying plugin implementers of a source being saved or deleted. Minor cleanup on sourceForm().

#701432 pounard, Will White: PHP 5.3: array_shift() expects parameter 1 to be array, null given in (...).

  scheduled tasks than 'import' and 'expire'.

This is a preemptory step to enable cleaner result handling and prepare the ground for Batch API use.

Don't log to watchdog when starting cron run.

Go back to scheduling 10 feeds per iteration. Breaks tests otherwise. Needs to be adjusted in extra step.