gweather: add gweather-xml.[c/h] files

Add gweather-xml.[c/h] files from libgweather. They were removed
with commit - 354f1aa9003ee08c6e63ecbaaa6b9179b9178184. This commit
add those files without any modification.
gweather: build with libgweather 3.7.3 or newer

- Bump gweather required version to 3.7.3. With this version
  gweather-xml.[c/h] files was removed.
- Use added gweather-xml.h file not from libgweather library.
- Update gweather-xml.c.
gweather: set correct column count for GtkTreeStore
gweather: update applet

- Completely port to GSettings removing remaining gconf usage.
- Fix preferences dialog:
  * Location list expanding to current selected location.
  * Settings for temperature, wind speed, pressure and visiblity
    units.
delete auto-generated legal.xml files
Makefile.am: Add MAINTAINERCLEANFILES
accessx-status: remove unneed gconf include
misc: delete ChangeLog.old files
misc: remove has_separator from *.ui files
misc: add more files to .gitignore
POTFILES.in: fix file name