Makes it possible to write a module as a python package.

Tries to clean up module imports to avoid lots of sys.path.inserts and
flattening of namespaces (particularly the merging of modules and
modules/lib).

Converts the map and mmap modules to be python packages.
Changed the module facility a bit to make it even easier to use
standard Python packaging/installation/path management for mavproxy
modules and still prevent naming conflicts.

Now when you issue "module load <module>" to mavproxy, it tries to
load a module named "mavproxy_<module>".  The modules that come with
mavproxy are still in the modules subdirectory, but now that directory
is added to sys.path.
fixes for new module layout from John Wiseman