Begin autoloading of the webpaste group

This will make it much easier for the user to discover available
options. It seems like a bad thing to autoload defcustom's but not
defgroup's.

This conclusion is based on what's have been done in haskell-mode:

Here they remove their autoloads of customs because it breaks shit:
f0affb46b8

But, what they don't remove is the autoload of the group:
f0affb46b8/ghc-core.el (L35)

So I'll assume that it's safe to autoload the group. This makes it
possible for users to run M-x customize-group webpaste without having
to either do a manual require or to use the mode before configuring.

This is a good improvement for discoverability for new users.

webpaste.el

@@ -40,6 +40,7 @@
 
 
 
+;;;###autoload
 (defgroup webpaste nil
   "Configuration options for webpaste.el where you can define paste providers,
 provider priority for which order which provider should be tried when used."