Frequency of tasks should be user-adjustable

[InsERT Webmaster]

I have a custom profile sync handler which has to run more frequently than every hour (the default value for the profilesync task). I can adjust the frequency by updating the relevant record in the core_tasks table but that change gets overwritten during an IPS update and is not the recommended approach anyway. A "Set frequency" option on the "Tasks" Admin CP page would solve this problem nicely