stored lastBlogId in preferences instead of sqlite

also rename methods for working with lastBlogId to use new style

git-svn-id: https://android.svn.wordpress.org/trunk@944 a6565c4b-a94d-4d28-bb26-aa9e5ab542c0
remove "add blog" from blog selector

Also greatly simplify WordPress.getCurrentBlog() and remove duplicate
logic from WPActionBarActivity.setupCurrentBlog().
Extend comment line length to 100 columns to match code line length.

git-svn-id: https://android.svn.wordpress.org/trunk@945 a6565c4b-a94d-4d28-bb26-aa9e5ab542c0