epub-page template: removed separate h1 $title$.

The title is now presumed to be the h1 that begins the body
(if there is one).
Removed unnecessary if around pagetitle.
Use pagetitle in title element for epub templates.
EPUB templates:  Use html5 doctype if epub3.
EPUB page template: Add epub (ops) namespace.
EPUB templates:  Added css, highlighting-css, quotes variables.

Removed hardcoded link to stylesheet.css.  Instead, the EPUB writer
now sets the css variable to stylesheet.css.
Removed epub-coverimage.html template.

Also removed TOC stuff from epub-titlepage.html.
Removed epub-titlepage.html.
Incorporated titlepage stuff into epub-page.html.
Split epub-page.html into default.epub and default.epub3.
EPUB templates:  UTF-8, lang variable, meta tags.
Added css to preserve space in <code> tags.

Thanks to Dirk Laurie.
Added tocdepth to latex template.
Added toc and toc-level to rst template.
toc-level -> toc-depth.
Added \placelist to context writer.

This selects TOC depth.
Added missing toc variable to default.rtf.
HTML template:  Add quotes styles if 'quotes'.
HTML5 template:  Made quote styles fit on one line.
Added conditional import of upquote package.

This fixes straight quotes in verbatim.