Subtitles: Change timecode matching mechanism for .srt files.

For timecode-based srt files, use the standard MythPlayer mechanism
for determining the current timecode, instead of directly using the
decoder and the current VideoFrame.
Fix mistake in 59512d5e9dad1cab2e5a5465dbeb7ae90fe5a128.
Add support for Miro v6.x. Fix watch video detection.

Signed-off-by: Raymond Wagner <rwagner@mythtv.org>
Fix Dvr::GetFilteredRecordedList() to return entries when no count is
given.  Previously, if filters were given without a count limit, no
entries would ever be returned.
A DVD menu is now defined as any time a NAV packet defines at least one button.  This should allow more flexibility to skip some intros.

Refs #11292
Quieten debug output when a DVD still frame is active
Apply timestretch setting to DVD stills.

Refs #11292
Only send position update during playback rather than the whole lot (bad copy/paste)
Allow to define an image notification with a URL or file path
Update description of osx-packager-qtsdk
Add new myth notification constructors

Allow to create a simpler notification, using strings only (title and author)
Add display of notifications stack.

Notifications will now be displayed on top of each other as a queue.
Non-registered notifications will be displayed for 5s minimum or per the duration requested.

Not themeable, no animations per say; all hard-coded for the time being.
Add optional argument to MythNotification constructor: details
Add notification for client connection/disconnection
Add notification for client connection/disconnection
Move creation of notification center so it will be last in screen stack.
Add missing include for uint32_t definition