Compatibility issues with Fx57+

SlimerJS has many errors during the startup. It doesn't work at all with Fx57+

To fix:

[x] require.js used to load xul-app does not exists any more
[x] issue in loader.js : String(this) does not work any more. It prevents to load commonjs modules
[x] calling webpage.open() with the post method does not work anymore
[x] webpage.onNavigationRequested seems to not be called for frames in a page
[x] many changes in nsIURI, which must be applied in all the source code:
- path has been replaced by pathQueryRef
- originCharset has been removed
[x] issues with WebPage.onAuthPrompt

laurentj / slimerjs