Adds pager option and uses $PAGER environment variable

Due to bat also reading the $PAGER environment variable, I first look to
see if bat is available. If it is, I use that. If it isn't, I use the
$PAGER environment variable. If that's not available, I use cat.

I also added the --editor flag to the help output which had clearly been
missed

Close #12

inc/file-management

@@ -117,6 +117,6 @@ viewFile(){
 
 	filename="$(findFile "$id")"
 
-	bat --color=always --style=full "$filename"
+	"$pager" "$filename"
 }