tk: cleanup & add PACKAGECONFIG

Changes:
- add PACKAGECONFIG "xft" enables XFontConfig features
- add PACKAGECONFIG "xss" enables XScreenSaver extension
- use ${BPN} and ${PV}
- use ${VER} intermediate variable for readability
- fulfill LIC_FILES_CHKSUM
- remove BINCONFIG_GLOB: inherit binconfig is not present, lib/tkConfig.sh paths are valid
- add SSTATE_SCAN_FILES, like it is done in tcl recipe (OE-Core)

Note: tcl and tk are sharing the same licence, tcl licence file in commited in OE-Core.

Signed-off-by: Matthieu Crapet <Matthieu.Crapet@ingenico.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>