Move Emakefile to app, fix compile

I moved cells to /apps/cells to work with reltool (even though it may
not have been necessary). This borked my customer Makefile compile so I
re-worked it to call "erl -make" on each apps/<app> directory.

The Emakefile needs to be copied into each app directory so Erlang knows
where to find the src files, where to put them, and what options to use.

$(foreach X, XS, foo) goes through each XS, puts the value in X and then
outputs foo, in which $(X) will output the value of X.

$(eval foo) outputs foo and the evaluates it as part of the makefile.
(e.g. so you can dynamically create targets and dpendencies)

The app_dirs function captures all the app paths in apps
(e.g. "apps/cells")

The app_dir_targets function does the same as app_dirs, but adds an
underscore on the end of the path so that make will never find it.

$(call foo) calls the foo function

What I do with all that is dynamically create an app/<app_name>_
target (i.e. with trailing underscore) so that make never finds it.
The recipe is then to cd into the app directory and call "erl -make".
erl -make will look for an Emakefile and compile whatever you specify
accordingly.

I don't need the old compile code but I'm out of time so I'll have to
cleanup later. The old systools release-building stuff won't work
either since I've changed the directory structure. I've switched to
reltools.