Move Apache log dir under %app_dir%

It's proven difficult to write an Apache vhost file that sanely places logs in both Ubuntu and MAMP. This revision moves the logs into a more concrete location (under %app_dir%) and allows customization (via the "log_dir" parameter).

Also: This commit allows one to turn off the vhost generation. If amp doesn't work well with a given system, you can fall-back to creating vhosts manually.