Add ability to use absolute paths for import

closes TryGhost/Team#2264
- Instead of relative paths, we can use absolute. It helps to keep code cleaner and don't worry about import when doing refactoring.
Relative paths require rewriting them in case a file is moved to another directory.

ghost/portal/jsconfig.json

@@ -0,0 +1,6 @@
+{
+    "compilerOptions": {
+        "baseUrl": "src"
+    },
+    "include": ["src"]
+}