FFMpeg Check, Readme Update

Adds a screen during installation to inform the user about FFMpeg and asks if they have it installed, will automatically set "useffmpeg" to true or false depending on what they choose. Includes readme with more user friendly steps to set everything up.
strictly speaking, this should be
````
return res.redirect('/install/server');
````

We can get away with it for now, but we should review this install script to be sure that we follow that guideline throughout. I know there are a couple of other instances where we are not doing this.