Changes to installation of pwbDashGUI

Several changes to how the pwbDashGUI is structured and installed. Now it should work after being installed centrally or into a virtual environment. A similar transition should be applied for other web apps in this repository.

The changes were:

• Switch setup.py to modern setuptools instead of distutils.
• Move package from webreports/pwbDashGUI/app to webreports/pwbDashGUI to be more consistent with Python conventions.
• All resources (clientside JS, CSS style-sheets, config files) are installed into the package directory and accessed via the pkg_resources module.
• Run script is placed into webapps/PWBTestingGUI.py.

Also a few tweaks to the GUI itself:

• Static styling of the GUI should be placed inside webreport/pwbDashGUI/assets/style.css
• A few fixes to the layout.