Move Lychee configuration to configuration file, replace lyheeignore and fix remaining false errors.

lychee.toml

@@ -0,0 +1,7 @@
+accepted = [200, 403]
+exclude [ 
+    '(?x).*profiles.ucl.ac.uk.*/thumbnail',   # People may not have a profile image.
+    '(?x).*github-readme-stats.vercel.app.*', # Returns 503 for some reason
+    '(?x).*127.0.0.1.*',                      # This is a local address
+    '(?x).*liveuclac.sharepoint.com/sites/*', # SharePoint pages will need UCL credentials.
+]