Genericize sync function name, hide access tokens from Web browser.

git-svn-id: https://plugins.svn.wordpress.org/tumblr-crosspostr/trunk@884469 b8457f37-d9ea-0310-8a92-e5e31aec5664
Rename sync setting name to more generic one.

git-svn-id: https://plugins.svn.wordpress.org/tumblr-crosspostr/trunk@884470 b8457f37-d9ea-0310-8a92-e5e31aec5664
Add new `init` action to migrate to new setting names.

git-svn-id: https://plugins.svn.wordpress.org/tumblr-crosspostr/trunk@884471 b8457f37-d9ea-0310-8a92-e5e31aec5664
Link to "Bring Your Own Content" in readme, version bump to 0.7.9.

git-svn-id: https://plugins.svn.wordpress.org/tumblr-crosspostr/trunk@884472 b8457f37-d9ea-0310-8a92-e5e31aec5664