Saner handling of dual-use as user and system-wide daemon:
 1) Make default config usable both for user and system-wide daemon:
  * Stop hardcoding file-store. See config part of patch 2001.
  * Recommend upstream to only hint about and rely on internal defaults
    (not explicitly set them) in config file. See patch 1001.
 2) Improve default file-store path when used as user daemon:
  * Patch default file-store to be ~/.local/share/Radicale/collections
    (to mimic XDG_DATA_HOME).
  * Recommend upstream to support resolving XDG_DATA_HOME for file-store
    (e.g. using python-xdg) and only use static path as fallback.
  * Adjust NEWS.Debian file accordingly.
 3) Improve default file-store path when used as system-wide daemon:
  * Recommend upstream to support overriding (XDG_DATA_HOME resolved or)
    static configured file-store path with a command-line option, to not
    depend on $HOME for system-wide daemon setups.
  * Adjust NEWS.Debian file accordingly.
 4a) Keep radicale as-is, and introduce system-wide daemon separately:
  * Move sysV init script and packaging scripts into separate
    radicale-daemon package, and start daemon by default.
  * Tidy NEWS.Debian file accordingly.
 4b) Switch to system-wide daemon by default, but allow overriding:
  * Ask with debconf if daemon should be enabled at start (default yes).
