Fix issues in Contract Development view (#5555)

* Better errors in contract dev

* Use RAW Git instead of Github Raw URLs (better CORS support)

* Network first for Solc list

* Don't use importScript n Worker // update rawgit to use CDN

js/src/util/solidity.js

@@ -52,21 +52,9 @@ export default class SolidityUtils {
 
   static getCompiler (build) {
     const { longVersion, path } = build;
-    const URL = `https://raw.githubusercontent.com/ethereum/solc-bin/gh-pages/bin/${path}`;
+    const URL = `https://cdn.rawgit.com/ethereum/solc-bin/gh-pages/bin/${path}`;
     const isWorker = typeof window !== 'object';
 
-    if (isWorker) {
-      return new Promise((resolve, reject) => {
-        self.importScripts(URL);
-
-        setTimeout(() => {
-          const compiler = solc(self.Module);
-
-          return resolve(compiler);
-        }, 50);
-      });
-    }
-
     return fetch(URL)
       .then((r) => r.text())
       .then((code) => {