v0.9 release checklist

[acobster]

• [ ] ~Refactor & test advanced search API #77~
• [x] Create a release/v0.9.0 branch (release/v0.8.0 is now defunct)
• [x] Fix form bugs #128 #129
• [x] Drop VVV support
• [x] Update get_context_with_post reference https://coniferplug.in/#more-helpers
• [x] Dismissable Alert #120
• [x] Lando rc.2+ dev environment
• [x] Site::disable_comments() convenience method
• [x] _wp_page_template shortcut admin column