Update install script

- Delete grails_completion.sh as there is dependency for gawk and this
  repository doesn't need to handle Grails
- Update osxdefaults script to run inside of a function; this issue was
  everytime the install script is run, it sources the .bash_profile and
  that includes anything in the bin/, so everything needs to be
  encapsulated in function scope
- Update gem install print statement for proper grammar/better reading
- Update install script to call `run_osx_setup` function

Issue: #9