Added major and minor modes.

This is for issue https://github.com/rejeep/ecukes/issues/103

The major mode is what the ecukes buffer itself uses and allows users to press g to rerun the tests and use n/p to go the the next/previous error (if any). After tests have been run, the modeline will display how many errors there were (in red if more than zero). 

The minor mode can be enabled in other buffers, like the elisp source which is being tested. This allows the user to run the tests with the keystroke C-c e (of course, users can change this). 

Also, both the major and minor mods provide an Ecukes menu with a Run Ecukes option. I normally ignore the menu, but some people use it I've heard. :-)