Fixes #1108. Turns out WP.com stopped returning the "wp.me" short link, so I removed all the network call that was used to get the link. Instead, we can just use Post.getPermaLink().

Also removed the icon from AlertUtil as it was the wrong Holo color.
Merge pull request #1109 from wordpress-mobile/issue/1108-share-post-fix

Fix post/page sharing