DevTools: Refactor build script to copy module files in debug_devtools mode

Currently, all module files are copied by the 'copies' GYP actions.
This patch makes build_applications.py copy the app HTML and directories
into the output directory.

R=dgozman, pfeldman@chromium.org

Review URL: https://codereview.chromium.org/646413002

git-svn-id: svn://svn.chromium.org/blink/trunk@183664 bbb929c8-8fbe-4397-9dbb-9b2b20218538