Python script to generate Chromoting's main.html.

With this change, it will be much easier to make changes to the UX (since
the dialogs will be easier to manage) and the set of JavaScript includes
will be guaranteed to match the gyp target.

This change also auto-generates the wcs_sandbox.html file.

BUG=
R=jamiewalch@chromium.org

Review URL: https://codereview.chromium.org/146903006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252135 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252135