Nested locations

Trying to replace `application` with nested location blocks.

Original comments after the first two commits:

1)
One thing I noticed: The overwrites within the inner "location" directives don't seem to be taking effect.

I have this config:

location /home {
user_apps on;
app_idle_timeout 30;

location /home/fereshteh/ShinyApps/04_mpg {
  app_idle_timeout 5;
}
But I see that for both of these cases the idle time is 30s.

2)
"application" is still a valid directive. I assume we want it that way for now.