Make svg short-code backwards compatible

With this change, the short-code should accept both a single positional argument as well as named arguments.

Signed-off-by: Sietze van Buuren <Sietze.vanBuuren@de.bosch.com>

themes/apertis/layouts/shortcodes/svg.html

-{{ $src := .Get "src" }}
-{{ $alignment := or (.Get "align") "center" }}
+{{- $src := "EMPTY" -}}
+{{- if .IsNamedParams -}}
+{{- $src = .Get "src" -}}
+{{- else -}}
+{{- $src = .Get 0 -}}
+{{- end -}}
+{{- $alignment := or (.Get "align") "center" -}}
 <figure style="text-align: {{ $alignment }};">
     {{ readFile (print "static" $src) | safeHTML }}
 </figure>
\ No newline at end of file