Making file extension optional, setting .sls as default for salt

Hey there!

Holidays, weekend, so why not dip my toes in reclass and add support for a custom file extension.
It's cosmetic, I know, but it will make it easier to convince my friends to use reclass ;)

NOT TESTED FOR ANSIBLE!!!

I don't use it (yet) so don't have anything setup to test if it works for ansible (so please full this down and see for yourself)


Now off to trying to add the directory support, that will probably be harder, wish me luck =D

Signed-off-by: Koen Schmeets <k.schmeets@gmail.com>