Fetchable dapps (#1949)

* Fetching dapp from github.

* Unpacking dapp

* Removing hardcodes

* Proper Host validation

* Randomizing paths

* Splitting into files

* Serving donwloaded apps from different path

* Extracting URLHint to separate module

* Whitespace and docs

dapps/src/apps/mod.rs

@@ -20,6 +20,9 @@ use proxypac::ProxyPac;
 use parity_dapps::WebApp;
 
 mod fs;
+pub mod urlhint;
+pub mod fetcher;
+pub mod manifest;
 
 extern crate parity_dapps_status;
 extern crate parity_dapps_home;