Fix for chef solo, .deb installation with gdebi, nginx tweaking

Hello,

As the cookbook wasn't working for me as it was, i've adjusted some things:

- rstudio is installed with gdebi rather than the APT repository, as the repository doesn't seem to host rstudio packages anymore
- The attribute usage apparently wasn't compatible with chef-solo, so i changed it a bit
- I was having problems with the nginx cookbook when using nginx_site without the parameters i added
- On first run, configuration is written on /etc but read from /opt, and shiny won't notice until it's restarted - so i changed shiny handling to restart shiny rather than reloading, so that the server is functional from the first run

Regards