[javascript mode] Properly parse quasi quotes without prefix

Closes #2472
[xml mode] Fix giant indentation when continuing an attribute on a long line

Closes #2473
[php mode] Add support for interpolated variables in double-quoted strings.
[php mode] Follow up on beb975f7e76c734044fa35a2c9a64b97f9eb5c94

Simplify some things, change a name.

Issue #2468
Merge branch 'master' of https://github.com/marijnh/CodeMirror