Fix AM_MAINTAINER_MODE as per guidelines

This shouldn't be the default mode, as universely agreed upon by
distributions.  It means that modifications to Makefile.am are not
automatically detected.  AM_MAINTAINER_MODE([enable]) is the recommended
solution, which disables it unless explicity requested during a
configure.
Start work on atcommands unit test
Add a CmdGenericAtCommand function to just pass a given AT string

This is useful for testing or running custom/proprietary at commands
Add a "Test" button to the GUI, that can run tests against the phone