Apply all the clang-tidy modernize-* fixes

Refactoring louloulibs and cmake

Use OBJECT libraries
Remove the louloulibs directory
Write FOUND variables in the cache

Fix an use-after-free

Because we “delete all node” and then we use the content of one of these
nodes we got earlier.

Introduce a XmlSubNode class that automatically adds itself into its parent

Include the Configure ad-hoc command on biboumi's JID  for fixed_irc_server

Because a jid like “freenode.example.org” is both the JID for the configured
IRC server, and biboumi’s JID.

fix #3175

Also store a reference instead of a pointer, in AdhocCommandsHandler

Use unique_ptr to store the XmlNode’s children

Also fix some constness things

XmlNodes are now always closed

Remove the close() method and closed attribute. Remove all the calls to
close().  (Save one bool per XmlNode, yay, and save a few ifs and some
useless function calls. At best it should be unnoticeably faster and lighter
and save a few keystrokes in the future)

louloulibs is directly included, instead of being a submodule

Because this is a nightmare to manage