MythZoneMinder: Add a popup mini player to show live camera views

This adds a jump point which will show a mini player that shows live views
from the ZoneMinders cameras.

The mini player works in a similar way to the music miniplayer so it will show
for 10 seconds then auto hide itself unless you press SELECT which will stop
the popup auto hiding. You can close the popup window at any time with ESCAPE.
The 1 key will cycle through the available cameras same as the normal live
viewer.

The next step is to auto show the mini player when an alarm is triggered in
ZoneMinder.
Default-wide: Remove duplicate 'basebackground' definition
MythCenter-wide: Remove duplicate 'basebackground' definition
MythCenter-wide: Add new 'miniplayer' window definition to zoneminder-ui.xml
Add support for explicitly recognising QAM-256 with DVB-T2. This _may_ help with scanning on devices that don't support 'auto' modulation detection.
Missed a change in [864d985]. Thanks to Karl Dietz for spotting the mistake.
MythZoneMinder: Add automatic popup notifications on alarms

Whenever ZoneMinder triggers a motion alarm for a monitor (camera) the popup
mini player will show with the alarmed monitor selected.

Only monitors that have notifications enabled will trigger the mini player to
show. You can toggle which monitors show notifications in the MythZoneMinder
console screen press MENU to show the options popup for the highlighted
monitor and make sure 'Show Notifications' is checked.

One use case would be a front door camera that triggers the popup to show
when someone is at the door so you know who it is before you answer it.
MythZoneMinder: Forgot to add a couple of files in [7c26cd6d185]
MythZoneMinder: Add the new notification_check to the default theme
ZMMiniPlayer: remove a stray member variable
ZMLivePlayer: pause the idle timer when showing the live camera's
ThemeInfo: add an optional 'basetheme' element to the theme info file

This element should be the name of the theme the theme inherits from if
applicable.
MythUIHelper: add any base themes to the search path and cache the result

This allows a simple form of theme inheritance where you could add your own
window or widget definitions to a new theme but still use everything else from
the base theme.

First the theme would be searched then any base theme if defined in
themeinfo.xml then the usual fallback to default-wide then default.

The next step would be allow windows and widgets in the new theme to inherit
from ones in the base theme so you would only need to change the elements
you need rather than having to completely redefine them in the new theme.
MythUIHelper: use the theme search paths to find a qtlook.txt

This allows a theme to fallback to any base themes qtlook.txt file.

We now also warn if one wasn't found.
MythUIHelper: use the theme search paths to find the widget background image

This allows a theme to fallback to using a 'BackgroundPixmap' or
'TiledBackgroundPixmap' image from a base theme.

We now also warn if one wasn't found.
Fix missed cases in earlier channel-specific rules change.

Refs #12267
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.

This reverts commit be72636b9e34b1b9fb032a1da578a742d562d0b9.
MythUIHelper: Fix loading some themes after 5cd97d7fd9

We use the directory name to load themes not the name in the theme.xml!
SSDP: Check that the peer address is available before doing the local network check.

Refs #12305
RingBuffer: Only decrypt vob files when located on a mounted DVD

Signed-off-by: Paul Harrison <pharrison@mythtv.org>