Updating Manga+Press to 2.8

git-svn-id: https://plugins.svn.wordpress.org/mangapress/trunk@863364 b8457f37-d9ea-0310-8a92-e5e31aec5664
Adding new banner image. Updating readme. Removing unneeded files.

git-svn-id: https://plugins.svn.wordpress.org/mangapress/trunk@863365 b8457f37-d9ea-0310-8a92-e5e31aec5664