HTML 5 parsing: Fix handling of xml:lang attributes on all elements

xml:lang is now mapped to a plain lang on all elements, not just <html>
...
FB2 Input: Fix paras with both id and style

FB2 Input: Fix a regression that broke conversion of FB2 files with
paragraphs having both a style and an id attribute. Fixes #1243709 [xls:attribute error in FB2 files](https://bugs.launchpad.net/calibre/+bug/1243709)
FB2 Input: Add support for note and cite back references

FB2 Input: Add support for note and cite back references. Link pairs of
type="note" and type="cite" now automatically generate the correct back
reference. Fixes #1243714 [Fb2 return link is lost when converted to mobi or epub](https://bugs.launchpad.net/calibre/+bug/1243714)
Merge branch 'master' of github.com:kovidgoyal/calibre

Conflicts:
	src/calibre/ebooks/oeb/polish/tests/parsing.py