Bug 1048927 - Enable 'add to home' for all web content. r=vingtetun

This enables the 'add to home' option for all web content and not just
e.me results.
Bug 1048927 - Use button.disabled in app chrome. r=vingtetun

Stop using data-disabled unnecessarily for button elements.
Merge pull request #22576 from Cwiiis/bug1048927-add-web-to-home-screen

Bug 1048927 - Enable 'add to home' for all web content. r=vingtetun