rename all snippet::xyz to just xyz

yes, another rename ... this time for good. since we took out the
top-level classes that were only used for configuring "general" config
files and creating .d directories, by merging them all into the config
class, we now have the space to move the snippets to the top level. this
will make it more intuitive to use those defines.

We'll keep related template files under a "snippet" directory, though,
since it helps to keep things uncluttered in the templates directory.

Signed-off-by: Gabriel Filion <gabster@lelutin.ca>