Update to version 1.7 see github for details

git-svn-id: https://plugins.svn.wordpress.org/wordpress-backup-to-dropbox/trunk@794309 b8457f37-d9ea-0310-8a92-e5e31aec5664
User memory instead of temp and remove old files

git-svn-id: https://plugins.svn.wordpress.org/wordpress-backup-to-dropbox/trunk@794352 b8457f37-d9ea-0310-8a92-e5e31aec5664