Improved the "installation" and "running" process

## Benefits
- User has to do npm install once and not every time (even though its not a big deal)
- User can pick once how they want to run night watch and only worry about the symlink on app's root.

## Short description of changes
- Removed npm install lines from all three shell scripts, that way when running the nightwatch we arent doing that extra steps each time.
- Auto creation of a symlink in app's root.
- Added setup.sh which allows users to pick one of the three options (which install the npm module at the correct location and created an appropriate symlinks which runs one of the three shell scripts)

## Boring, long description of changes

I added a setup.sh file that lets users decide for their project how they want nightwatch to be run. Once they pick the appropriate answer, the nightwatch@0.5.3 (or something) is installed at the appropriate location (I think for the package option, the location is slightly varied) then a symlink in the app's root is created which runs the older "launch_nightwatch_from_X.sh" shell scripts.

I also removed the npm install lines from the older shell scripts as they are no longer needed.