Themed menus: clean up the classes/interface.

This prepares for converting more TV Playback menus into equivalent
themed menus.  Refs #11533
Simplify action names in the cutlist editor.

Many of the cutlist editor actions contain the frame number as one of
the components of the action string.  This is unnecessary because the
frame number is always the same, i.e. the current frame number, when
the action is handled.  These action strings are now simplified, and
several methods that took the frame number as an argument are also
simplfied since that argument is redundant.  Refs #11533.
Correct a small typo in a menu description.
Themed menus: Implement the cutlist editor menus.  Refs #11533

Provides an implementation of the main cutlist editor menu
(menu_cutlist.xml), and the exit dialog menu (menu_cutlist_exit.xml).

There is a slight change in behavior - pressing SELECT within a cut
region brings up the entire cutlist menu, rather than a subset.  The
original code suppresses the submenu entry at the end on the SELECT
action.  The original behavior could be restored by adding a third
cutlist menu, or by designing a way to pass extra state to the menu
builder.

To make this work seamlessly with existing action handlers, clumsy
action names like DIALOG_CUTPOINT_NEWCUT_0 are preserved.  This will
need some cleanup.

There is one remaining cutlist-related menu that could be implemented
- the "already editing" dialog.
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.