Title slide: align all four corners, make QR codes scalable

qrcode::generate_svg() paints the code into a fixed 300x300 canvas and
emits no viewBox, so the svg could not be resized by CSS: given a smaller
box it kept drawing at full size and only its top left corner stayed
visible.  qr_svg_fit() adds a viewBox cropped to the dark modules, so the
code scales to whatever box it is placed in and its quiet zone becomes
the surrounding layout's business -- the white plate behind the title
slide's code, and padding on a.qrcode elsewhere.

With that in place all four title-slide corners share one 8px inset
measured to the visible ink: IDS (plus partner) logo top right, website
QR top left, funder logo bottom left, WGL membership logo bottom right.
The funder logo previously sat 20px lower than intended, because
reveal.js' default image margin adds itself to the offset of an
absolutely positioned image.

Also point the documented repository url at gitlab rather than gerrit,
and give the ids example deck an Overview slide.

Change-Id: I27447527345b71572a9e952bc21f542eba1ec352
diff --git a/examples/ids.Rmd b/examples/ids.Rmd
index d657904..d303aff 100644
--- a/examples/ids.Rmd
+++ b/examples/ids.Rmd
@@ -6,7 +6,7 @@
   - name: John Doe
 institute: "IDS Mannheim"
 date: "`r paste0('Mannheim, ', Sys.Date())`"
-website: "https://korap.ids-mannheim.de/gerrit/IDS-Mannheim/revealjs"
+website: "https://gitlab.ids-mannheim.de/ids/revealjs"
 partner_logo: "logos/clarin-logo.svg"
 funder_logo: "logos/text-plus-logo.svg"
 output: 
@@ -35,6 +35,8 @@
 library(DT)
 #source("https://gitlab.ids-mannheim.de/ICC/2023-07-20-ICC-ICLC10/-/raw/master/R/common.R")
 ```
+## Overview
+
 # Introduction
 
 ## R Markdown