mod_proxy_uwsgi: Add in UWSGI proxy (sub)module

trunk patch: http://svn.apache.org/r1810358
             http://svn.apache.org/r1810362
             http://svn.apache.org/r1810363
             http://svn.apache.org/r1810365
             http://svn.apache.org/r1810447
             http://svn.apache.org/r1816919
             http://svn.apache.org/r1816922
             http://svn.apache.org/r1818013
             http://svn.apache.org/r1818280
+1: jim, icing, minfrin
icing: tested on ubuntu 16.04 with a simple uwsgi python app.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1824184 13f79535-47bb-0310-9956-ffa450edef68