Added fetchers concept: seperate scripts to fetch the feeds

Fetchers claim to be a certain client. They try to send the same
headers as the original client. That's better than a simple curl request
with a fake user agent, because curl doesn't send the other headers like
the original client and therefore its traffic stands out.

fetchers/chrome_agents

@@ -0,0 +1 @@
+User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.78 Safari/537.36