Remove some stray references to the ImageThumbGenThread from the frontend which caused a segfault.
mythzmserver: fix the debug output telling us which mmap files we opened
MythZoneMinder: finish the support for ZoneMinder >= 0.26.0

All combinations of capture palette and target colour space should now be
supported. This also moves all the processing to mythzmserver and always
passes RGB24 to the plugin.

Note: bumps the protocol version so both mythzmserver and the plugin need to
be updated.
Improve the performance of Live TV embedded in the Program Guide.

Most of the Program Guide's DB and backend queries are moved out of
the UI loop into a background helper thread, to minimize the chance
of the embedded Live TV window stuttering.

More work can and should be done to pre-cache scheduler data and
channel tuning status, and to have the backend invalidate/update it
when there are changes.

The background computation introduces some guide navigation UI
oddities, where the expensive-to-compute elements (the list of
channels) update on the screen slower than other elements.

There is still some slight stuttering on a single-core ION frontend,
but most frontends should see a vast or complete reduction in Guide
navigation stuttering.

Refs #11020
WebFrontend: Add filtering by title to the Recordings page. The services API will need some changes before I can support filtering/grouping by category which some of us prefer.
MythZoneMinder: fix typo
Cleanup and simplify the HLS Recorder.
MythDownloadManager has a memory leak, which can be terminal when used by

the HLS Recorder.  Add a simple MythSingleDownload class which uses
QNetworkAccessManager directly to avoid the leak, until it can be found and
fixed.
The classes defined in httplivestreambuffer.cpp were originally designed for

HLS playback, and are inefficient for recording.  Create a new
recorder-specific HLS processing class called HLSReader.  Since it is
specifically designed for recording, HLSReader is more efficient and faster.
Add missing 'class' to friend declaration.
Load category_type into ProgramInfo for recordings
Quiet some HLS logging
Services: Add UnDeleteRecording() method. Name may be subject to change.
WebFrontend: Add support for undeleting recordings; Show a message if the guide/recording list is empty; A few bug fixes and cosmetic tweaks.