Add Commons logo to installer

Re-titling with the actionable item.

I tried to borrow code from Commerce Kickstart to set the commons_origins theme during install, but for some reason it's not quite working (the logo is set, but elsewise it looks like Stark). Here's an in-progress patch; I'll try and debug it more tomorrow.

(just the _commons_set_theme part; the rest is other UX issues gummed up with it... I need to teach myself git stash tomorrow, too. :P)

The AT/Origins theme settings probably haven't taken effect until we do

drupal_form_submit('system_theme_settings', $form_state);

in commons_install.

I'd commit this as a progress commit but we refactored commons_install_tasks_alter() with #1869468: During installation, users were mildly annoyed they immediately had to skip past default English language; streamline this?. We're also expecting a shiny new logo "soonish".

Restoring 7.x-3.x version property.

clarify again