Allow local logs for cat-log

[ScottWales]

Add a configuration item c.CylcUIServer.force_remote_logs defaulting to True (matching existing behaviour)

When True, cat-log will use the --force-remote option to always fetch from the remote Cylc server

When False logs will only be fetched if they are not present on the local server

Fixes #506

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• Tests are included (or explain why tests are not needed).
• CHANGES.md entry included if this is a change that can affect users
• Cylc-Doc pull request opened if required at cylc/cylc-doc/pull/XXXX.
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

As mentioned in #506 there shouldn't be a need to make this configurable, someone needs to go through the cat-log code and make any required adjudgements to ensure that the command uses the local files when available and file listings remain correct. This isn't something I've had the time to do so far.