cylc poll-all: no options given then poll all

Closes #1177

Tests added.

Polls all tasks when no options are given at the command line.

Note that in my environment including on master tests/cylc-show/03-clock-triggered-non-utc-mode.t fails.
Would this break the old behaviour, i.e. if `ids` is a list of task IDs to poll?

Do we need to poll `retrying` and `waiting` tasks? I would not expect them to have jobs that need polling.