Realtime rebuild

## Problem
Because Revel receives file change events when receiving HTTP requests, 
Revel does not rebuild an application until a browser reload or something.

## Solution
But you can start to rebuild the application when the file is changed if you watch file change events in real time.
So I created goroutine to receive them.

Because a select statement without default case waits until receiving events, its performance didn't become worse.
Ah, I think `MainWatcher` is just used for the routes file.