Add basic cmake build instructions.
Delete empty folder templates.
Delete rpm stuff (kshowmail.spec and build-kshowmail folder).
Rework of the README and AUTHORS files.
Add BUGS file.
Move the kshowmail.desktop file into XDG_APPS_INSTALL_DIR directory,
see TDE/tde#26 and bug 2408.
Some cosmetics.
Signed-off-by: gregory guy <gregory-tde@laposte.net>