Removing the platform file

ncc is a very strange step in the build process. It is basically a
magical perl script that sets a bunch of include directories, but is
really just another opaque layer to figuring out how tinyos is getting
built. While trying to re-write it to make it a bit cleaner and smarter,
I had a realization: Why are include directories and nesc flags (which
are used to compile code) smack dab in the middle of a src folder
(tos/platforms/<platform>/platform)? Why isn't all of that contained in
the make system (where you would expect it to be? In fact, why do we
need these magic files (platform, family, sensor) at all?

This commit addresses these questions by starting to move what was in
the platform (etc.) files into the make system. In this way, X.target
files include Y.platform files, Z.sensor files, (etc.) in order to get
all of the relevant flags without needing to write perl code.

Also, tos-sub-tosdir tool makes the %T flag magical. Instead of just
being replaced with $TOSDIR, it is replaced with all of the $TOSDIR
paths that point to actual folders. This allows for first class support
for out of tree platforms, as they will be able to use the %T syntax and
have it just work. This is convienent because if the platform ever gets
moved to tinyos-main it will just work.