Contact Form: do not display the logged in user's details

Can be overwritten with the jetpack_auto_fill_logged_in_user filter
Fixes #694l
Contact Form: fix spacing

See https://github.com/Automattic/jetpack/pull/725#commitcomment-6888035
Site Logo: Sanitize header text classes for output.
Merge branch 'master' of github.com:Automattic/jetpack into site-logo-escaping
Merge branch 'site-logo' into site-logo-escaping
Move Jetpack endpoints to individual files.
Site Logo: Remove redundant `description` property, which is already in WP_Customize_Control.
Merge pull request #726 from jeherve/grunion_noemail

Contact Form: do not display the logged in user's details
Improve update_core function.

By default try to find the latest core version.
Restore single upgrade version.
Oops copy and paste.
Fix update plugin test.
Add Update Core Test

Leaving it commented as it could change the state of the site.
Merge pull request #1144 from Automattic/jetpack-endpoints-refactoring

Jetpack endpoints refactoring. Move Jetpack endpoints to individual files.
Code Style: Add braces and tidy whitespace.
Swap function into conditional.

This way, a bad $attachment_id won’t break things.

Fixes #1143
SSO Don't recreate a user account if they have one

If match by email is off, and they have an account already, don’t make
them a new one.

Props @fjarrett for reporting the bug.
Fixes a bug introduced in e91dd2d3f5db31f9a9ae6a1b0809632012775ecc
Merge branch 'master' into site-logo
Merge branch 'site-logo' into site-logo-escaping
Site Logo: Reset the logo setting if the current site logo gets deleted from the media manager.