On new Doc, cascade permissions settings if Read setting is changed

This will make it more convenient for users who want to change the default,
lax privacy setting to something more secure.

If, at some point during the pageview, you manually change one of the other
permissions settings, the cascade will no longer take place. This prevents
your manual settings from being overwritten.

Props @dcavins

Fixes #306
Fix the wonky tabindex on Text mode when editing a Doc

There's some weirdness in the way that tabindexes are set up when using Text
mode (vs Visual mode) of the WP editor. Namely, when you hit Tab from the
previous field, you have to cycle through all the styling buttons before
getting to the actual doc content.

As a workaround, I've added some code that detects tab-outs from the
Permalink field, and when one is detected, it sends focus to the end of the
doc_content textarea.

Fixes #311. Props @dcavins for the original patch.
Merge remote-tracking branch 'upstream/1.4.x' into 1.4.x