Add support for explicitly recognising QAM-256 with DVB-T2. This _may_ help with scanning on devices that don't support 'auto' modulation detection.

(cherry picked from commit 864d985786a6f0f0fe2b93b4539c12ee2b0e09e2)
(cherry picked from commit 376955a091dbf69f7cc233fa1bf3255401e80367)
Fix missed cases in earlier channel-specific rules change.

Refs #12267

(cherry picked from commit d3f5031e08c0a9e0fa783310afa4d293bacf6ce0)
Revert "Prevent --syslog, --logpath and --enable-dblog if --nologserver is used"

Seems those options are valid for --nologserver. That option just means don't run
the external mythlogserver but do the logging internally.

Refs #11992.

This reverts commit ec06dfba8e22008ac97af81f997e9b521eca62ae.
Merge branch 'fixes/0.27' into stable/0.27