Change static_page public dir to 'public_dir' in app->config

Instead of using $app->config_location/public use the public_dir
specified in app->config->{public_dir}
Refactor error_template.t test

Change Plack::Test to OOP style

change test app setup from $ENV based and engine-local settings to
standard setting via 'set views' and 'set public_dir'

Separate the test app into two apps, one which has it's own custom error
templates defined and one which has not.
move location
reflect change
Merge branch 'pr/error_static_page_pubdir'