Logging changes.

- Have fppd load saved LogLevel and LogMask settings at startup
- Remove references to old 'verbose' setting
- Add a UI for changing the log level and mask
- Move parsing of --log-level and --log-mask options to helper
  functions in log.c.
- Rework command socket handling of LogLevel and LogMask changes
  to make it easier for UI to change these on the fly without
  having to duplicate code or spawn fpp.

As part of the above:

- Add fppjson.php.  This is like fppxml.php, but returns JSON
  which is much easier to deal with in JavaScript and PHP since
  there are helper functions which convert between JSON and
  native data types.  For now, fppxml.php stays and has not
  been converted, but the groundwork is layed for future additions
  to use JSON and allow future conversion from XML to JSON of
  existing calls.
- Add JavaScript and PHP arrays to track all settings stored in
  /home/pi/media/settings config file.  settings[SETTING_NAME]
  and $settings[SETTING_NAME] in JavaScript and PHP respectively.
  In the future, this will allow us to get rid of a lot of the
  "global $varname" type lines sprinkled through the code in
  favor of one "global $settings" line.  It also means we don't
  have to add new variables each time we add a new setting to
  the config file, the new setting is automatically added to
  the settings arrays.