PLT-1800 Load server side locale from the config.json (#3092)

* PLT-1800 Load server side locale from the config.json

* Add support for locales with country specifics

* Fix localization on served locale file as plain/text

webapp/package.json

@@ -27,8 +27,9 @@
     "react-bootstrap": "0.29.3",
     "react-custom-scrollbars": "4.0.0-beta.1",
     "react-dom": "15.0.2",
-    "react-intl": "2.0.0-rc-1",
+    "react-intl": "2.1.2",
     "react-router": "2.4.0",
+    "react-select": "1.0.0-beta13",
     "react-textarea-autosize": "4.0.1",
     "superagent": "1.8.3",
     "twemoji": "2.0.5",