cylc test-battery: expand battery 2

Batch of additional tests 2.

This adds testing for:
 * dummy mode (and associated correction in documentation)
 * cylc cycletime - parsing, printing and offsetting
 * timeparser.py - wrapper to be used (potentially) for ISO8601 + fix for `CylcError` reference
 * basic database testing to ensure messages being recorded and schema hasn't been broken
 * jinja2 expanding, validation and include behaviour