add correct COPYING file

Commit 1ee9bd740898d3b7438e4e8bb06318cb823af6d5 added wrong
COPYING file. Fix it by adding GPLv2 COPYING file.
upgrade LGPL license to GPL

GNOME Applets are licensed under GPL (v2 or later) so change LGPL
license to GPL. (LGPL license allows this move)
fix incorrect FSF address
add license header for two gsettings.h files

These files was created by me.
mini-commander: add missing license headers

Only three .h files did not have license header. Add same license
headers that are available in .c files.