[Core] Configure E1.31 Bridge mode to allow reception on both eth0 and wlan0

Previously bridge mode would only listen for multicast on the first
configured interface which could be wlan0 if it was the default
route.  This commit changes the code to call setsockopt() for both
eth0 and wlan0 if they are configured to allow E1.31 reception on
either interface.
[Core] Add debug message to help tracking down a bug
[UI] Better handling of git describe output for version string
[GPIO] Add support for Normally Closed (NC) GPIO Inputs
[Playlists] Bugfixes and playlist control enhancements.

Fix a few bugs in the playlist/schedule code, some recent, some old.

Add support for controlling a running playlist via the 'fpp'
command line utility.

    To jump to the next entry in the running playlist:

    fpp -c next

    To jump to the previous entry in the running playlist:

    fpp -c prev

    To stop a running playlist:

    fpp -c stop

    To stop a running playlist gracefully:

    fpp -c graceful

These will be helpful with event scripts and allow events to
be essentially blocking by inserting a pause after the event in
the playlist and having the event script call "fpp -c next" when
the event is over to end the pause early and resume playback.
[GPIO] Add 200ms debounce timeout for GPIO Inputs.
[Help] Add help page for Memory Mapped Channel Block screen
[Help] Allow pressing F1 for popup help and change help link
[Scheduler] Fix bug in midnight rollover if no schedules created.

Bug would cause a segfault trying to play a schedule/playlist that
did not exist.
[UI] - Network settings help file
[UI] Network Config Help File Added
[UI] Wrong extension
[UI] Wrong Extension
[UI] Rename help files from .html to .php
Merge branch 'master' into stage
[UI] Cleanup.
Merge branch 'stage'
Merge branch 'stage'
Merge branch 'stage' into v0.4.0