Reverse Proxy SSL Support / Security Improvements

Shell scripts and configuration files are currently copied into ht root folder and accessible via apache if this container is linked to the web. At the least this reveals system configuration information.

Added a line to wp-config.php that allows the instance to support reverse proxied ssl connections.
I just ran a test build on this and got: `/usr/src/wordpress/docker-entrypoint.sh: line 117: syntax error: unexpected end of file`.  It worked when I unindented the heredoc.

Also, @tianon had you put that in the wrong spot (it was supposed to be in the `if [ ! -e wp-config.php ]` so that we  get the default config too.

I already made these changes locally, so I'll just merge in your PR with my changes too.

Thanks for the contribution @drewwestphal!