add a settings entry for skin settings in Appearance, enabled if SkinSettings.xml is available in the skin. Skinners should move their skin settings into this file, and remove links to skin settings elsewhere if they are no longer required.
[confluence] move skin settings to SkinSettings.xml
Fixed: [Confluence] Don't assume TV Shows return a poster for their scrapped thumb anymore because apparently that changed recently and they now get banners again
build: give env optim flags precedence

Fixes builds like: 'CFLAGS=-O3 ./configure'
[droid] don't disable optims, it disables ffmpeg optims as well
Merge pull request #1622 from jmarshallnz/skin_settings

Skin settings to a button in Appearance, under skin chooser
don't fill in the thumb or icon in CApplicationMessenger::MediaPlay - that's not it's job
move video and music thumbloaders to their own .cpp/h files
there is no reason for the recently added job to hold a CVideoThumbLoader member
there is no reason for the video info dialog to hold CVideoThumbLoader or CGUIDialogProgress members
cosmetics: cleanup CGUIListItem's art functions a bit
adds AppendArt to CGUIListItem
drop backward compatibility for artist art - a rescan of music is required anyway, which will yield this moot
add cache of album art and show art in the music and video thumbloaders, to reduce repeated database queries
initialize the music and video thumbloaders in the recently added job to take advantage of database and art caching
use a list of allowed types rather than disallowed types of library items to filter out items that don't require further processing.
Merge pull request #1609 from jmarshallnz/cleanup_video_music_thumbloaders

Cleanup video music thumbloaders
Merge branch 'master' into master-dev

* master:
  use a list of allowed types rather than disallowed types of library items to filter out items that don't require further processing.
  initialize the music and video thumbloaders in the recently added job to take advantage of database and art caching
  add cache of album art and show art in the music and video thumbloaders, to reduce repeated database queries
  drop backward compatibility for artist art - a rescan of music is required anyway, which will yield this moot
  adds AppendArt to CGUIListItem
  cosmetics: cleanup CGUIListItem's art functions a bit
  there is no reason for the video info dialog to hold CVideoThumbLoader or CGUIDialogProgress members
  there is no reason for the recently added job to hold a CVideoThumbLoader member
  move video and music thumbloaders to their own .cpp/h files
  don't fill in the thumb or icon in CApplicationMessenger::MediaPlay - that's not it's job
  [droid] don't disable optims, it disables ffmpeg optims as well
  build: give env optim flags precedence
  Fixed: [Confluence] Don't assume TV Shows return a poster for their scrapped thumb anymore because apparently that changed recently and they now get banners again
  [confluence] move skin settings to SkinSettings.xml
  add a settings entry for skin settings in Appearance, enabled if SkinSettings.xml is available in the skin. Skinners should move their skin settings into this file, and remove links to skin settings elsewhere if they are no longer required.