Various fixes

Hi Boone,

First of all, apologies for doing this under the 'master' branch.  I just noticed there was a '1.8.x' branch, but I guess you could cherry-pick the commits!

Main fixes are:

* Group member promotion / demotion and blog role syncing (#16, #13) - 81b6aa8 + c3a758a
* Blog validation (#14) - 0f421c9
* [Homepage redirection](https://wordpress.org/support/topic/redirect-goes-to-wp-admin) - e6a4a0a, 1952a49, 55fb215

Miscellaneous:
* #18 - 8b706bc
* #17 - 94e0af9

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The bundled themes are a mess.  I don't think we should support them going forward because we don't force users to use bp-default anymore as of BP 1.7 and both P2-BuddyPress and the bp-groupblog theme are deriviatives of bp-default.

Let me know if you want me to look at any other issues for BP Groupblog.