cycle points of inserted tasks need standardising

[hjoliver]

Somewhat related to #1014 - tasks inserted with cylc insert do not have the given cycle point converted to standard representation (and time zone) before insertion into the task pool. Spawned successors do have the correct representation.

[arjclark]

@benfitzpatrick - along similar lines (probably related), it's been reported that inserting within the cylc gui without the Z on the end of the time to insert at seems to result in two copies of a task being inserted one with and one without the Z (this may just be how the logs read rather than what's actually happening).