File handling was broken on Windows. This commit contains a revision of the path handling with separation of file paths and urls where needed.
There may be remaining issues and there may be better ways to do this, but it is easier to start that refactoring job with a set of passing tests.
Fixes #687
Fixes #660
Following issues are fixed
1. Can't access fields and methods specified in GroupBy call
2. PagesGroup doesn't contain Pages. It's always empty.
3. When GroupBy is called with Section key, it doesn't work as expected
