Themed menus: clean up processing of includes.

Removes the ephemeral m_recursionLevel field from MenuBase, and
handles the guarding against infinite include recursion through method
arguments.  Refs #11533.
Added missing initialisation of MHEG member variable that sometimes caused (non-MHEG) video playback to pause at the end.

Signed-off-by: Stuart Morgan <smorgan@mythtv.org>
Fix a performance warning from cppcheck.
Fix cppcheck warnings.

This fixes an apparent mistake in
a1eac715a9ff2f1d18cfddc69f49664c57150735.
configure: modify the taglib check so it doesn't add anything to extralibs
Formatting cleanup of mythsystem.h
Formatting cleanup of mythsystem.cpp
Add some code review comments on the MythSystem interface.
Add TMPMAK to .gitignore
Fix potential memory leak in MetaIOID3::readAlbumArt() on error. Coverity 1023890
Themed menus: Allow an item to always be set as current.

The current="active" attribute is extended to allow current="y", so
that a menu item can always be set as currently selected when entering
a menu.  The exception, as before, is when returning from a submenu,
in which case that submenu is always set as current.

Synonyms for "y" are anything starting with "y", anything starting
with "t", or "1".

Refs #11533
Fix bug in mythtranscodes clean-cutting mechanism

One of the clean-cut methods interacted badly with mythtranscodes
synchronisation algorithm and would sometimes cause frames from
cut segments to be kept. This commit fixes that bug

Refs #11531
MythUIWebBrowser: show the keyboard input status on the status bar when toggled
MythMusic: allow the last playtime to be set to a specific time
MythMusic: also remove cd tracks from the music_map when cleared
MythMusic: handle a MUSIC_METADATA_CHANGED MythEventMessage in the musicplayer

This event message can be sent by any client that changes a tracks metadata
to allow any FE's to update there copy of the metadata and update any screens
showing the tracks info.
Themed menus: allow Undo/Redo options to always be displayed.

This changes the treatment of the Undo and Redo menu items in the
cutlist editor so that they can always be displayed, even when no undo
or redo action is available.  By default, unavailable undo/redo
actions are hidden via the show="active" attribute.
Themed menus: Add a compact version of the cutlist menu.

The compact version is taken from menu_cutlist_compact.xml.  Revert
the addition of menu_cutlist_exit.xml, as there's really no need to
allow such customization.  (Users may want to manually remove
menu_cutlist_exit.xml from their installation directory.)  Add the
ability to take a menu description from an internal string rather than
an external file.  Refs #11533.
Remove qmake dependency on ffmpeg file that no longer exists.
Get mythbrowser to compile in Qt5 (won't do much).