Possible fix for #50
Small refactoring for http storage
Small refactoring in sync
Fix #51
Add test case for #49
Possible fix for #49

  - Radicale incorrectly unquotes URLs
  - Older versions of radicale are so buggy they fail to look up items
    with url quotes in them.
  - ownCloud/SabreDAV follows the rebustness principle such that it
    takes anything, but returns properly encoded URLs.

Conclusion: Send broken, unquoted URLs, because both sides seem to be
happy with them. As wrong as it might seem, it works.