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

• [x] I have read CONTRIBUTING.md and added my name as a Code Contributor.
• [x] Contains logically grouped changes (else tidy your branch by rebase).
• [x] Does not contain off-topic changes (use other PRs for other changes).
• [x] Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• [x] 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.