Insert a BOM check for import and file upload

* Similar to @janekptacijarabaci fix in greasemonkey/greasemonkey#1940
* Fix compliance with STYLEGUIDE.md and usage of pre-initialized identifiers
* Currently **do not** propagate BOM with meta routine or user.js source with and without installation count increment
* BOM currently shows up in Ace as a exclamation triangle with "This character may get silently deleted by one or more browsers"

**NOTE**: Many thanks to the report by @cvzi and applies to OpenUserJS#200 and partially outlined in OpenUserJS#198.

controllers/scriptStorage.js

@@ -227,11 +227,12 @@ exports.getMeta = function (aChunks, aCallback) {
   var str = '';
   var i = 0;
   var len = aChunks.length;
+  var header = null;
 
   for (; i < aChunks.length; ++i) {
-    var header = null;
+    header = null;
     str += aChunks[i];
-    header = /^\/\/ ==UserScript==([\s\S]*?)^\/\/ ==\/UserScript==/m.exec(str);
+    header = /^(?:\uFEFF)?\/\/ ==UserScript==([\s\S]*?)^\/\/ ==\/UserScript==/m.exec(str);
 
     if (header && header[1]) { return aCallback(parseMeta(header[1], true)); }
   }

controllers/user.js

@@ -925,7 +925,7 @@ exports.userGitHubImportScriptPage = function (aReq, aRes, aNext) {
 
       if (options.javascriptBlob.isUserJS) {
         //
-        var userscriptHeaderRegex = /^\/\/ ==UserScript==([\s\S]*?)^\/\/ ==\/UserScript==/m;
+        var userscriptHeaderRegex = /^(?:\uFEFF)?\/\/ ==UserScript==([\s\S]*?)^\/\/ ==\/UserScript==/m;
         var m = userscriptHeaderRegex.exec(aBlobUtf8);
         if (m && m[1]) {
           var userscriptMeta = scriptStorage.parseMeta(m[1], true);