qutebrowser: Switch out shaarli integrations for linkding

Use linkding for the 'l' search engine and add a linkding adding
userscript which we use with the ";s" keymap. Add user command
'add-linkding'.

qutebrowser/data/userscripts/linkding_add.sh

@@ -0,0 +1,27 @@
+#! /usr/bin/env bash
+#
+# Send current page/link to a shaarli instance.
+#
+# Can be used for sending the current page via:
+# :spawn --userscript shaarli_add.sh
+# for sending an arbitrary page passed as argument:
+# :spawn --userscript shaarli_add.sh https://myinterestingpage.com
+# or for sending a hinted link:
+# :hint links userscript shaarli_add.sh
+#
+# Configure your shaarli instance with this:
+INSTANCE="https://links.martyoeh.me"
+
+# send page to shaarli instance and open the 'post' page to edit it
+if [ "$#" -gt 0 ]; then
+    BM="$INSTANCE/bookmarks/new?url=$*&auto_close"
+else
+    BM="$INSTANCE/bookmarks/new?url=$QUTE_URL&auto_close"
+fi
+
+if [ -n "$QUTE_FIFO" ]; then
+    echo "open -t -r $BM" >>"$QUTE_FIFO"
+else
+    xdg-open "$BM"
+fi
+