setting up composer to install RMT script to vendor/bin/RMT, adding option to skip creation of projectroot/RMT during init 

fixes #59

Aloha, here a PR to change the behaviour in the way as described in #59.
what i changed:

- i changed the RMT script thats coming with RMT to use getcmd() instead of __DIR__. This is probably the only critical change, since that means if you release RMT itself from any other dir than its project root, it will not work.
(This is not the case for the RMT that gets written to project root of projects using RMT who are not skipping the creation of the convenience script)
- i added RMT to the composer json, so it will be linked in vendor/bin/RMT (as composer suggests)
- i added an configonly option to the init script, where a yes-no will be asked on wether to create or not create the RMT convenience script (the one in project root)
- i modified the tests so they set configonly to n on commandline, making it run with the exactly same behaviour as before


then there are a few "fixes" i sneaked in that i saw along the way (basically just beautyfixes:
- i deleted 2 "use" in scripts that where not needed
- i changed an exec() calling chmod to using php's chmod command