Fix styling and move towards standard TemplateResponse

[skjnldsv]

• Requires new RENDER_AS_CLEAN template on server that provide bare minimum styling (variables only) and core js

[jancborchardt]

For reference, this is the small style modifications I experimented with – let’s see if they still work when we update pdf.js:

// Transparent background
body {
	background-color: transparent;
	background-image: none;
}

// Semi-transparent background for toolbars
#toolbarContainer,
.findbar,
.secondaryToolbar,
#toolbarSidebar {
	background-color: rgba(0, 0, 0, 0.85);
	background-image: none;
}