git: Merge .gitignore files into a single file

git: Merge .gitignore files into a single file

We already track a lot of files over the whole directory structure
in the main .gitignore file.  But a few additional ones had been
added into some of the subdirectories.

This unifies all these files into a master file for the whole project,
making it easier to know where to look at and edit if changes needs
to be done.

Signed-off-by: David Sommerseth <davids@openvpn.net>
Acked-by: Steffan Karger <steffan@karger.me>
Message-Id: <20170120210457.3383-1-davids@openvpn.net>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg13916.html
Signed-off-by: David Sommerseth <davids@openvpn.net>
(cherry picked from commit d14b3c60c7796736e07bc3cddb0ab3a58475793e)