Don't load ImageBrowser plugin on SN or Touch
Update note about installing required perl binaries. Point to github
instead of svn now.
Merge branch 'public/7.7' into public/7.8

Change-Id: I565cfb7914a40945079ab3e1c17b7b996117d4f9
Let clients register artwork sizes they want to be pre-cached

- clone prefs hash before dealing with it, or the change handler will
fail
- don't register change handlers in modes where they are not supported
- trigger an artwork scan when a new spec is added
Initialize customArtSpecs preference
Don't duplicate default artwork resizing specifications
Merge pull request #1 from Logitech/public/7.8

Public/7.8