Add dimensions middleware

EXAMPLE USAGE:

* Use it with no parameters to get all the dimensions in the query: `app.get('/', dimensions(), function(req, res, next){})`
* Use it with an array of accepted values: `app.get('/', dimensions(['year', 'location']), function(req, res, next){})`
* Use it globally: `app.use(dimensions())`

libs/middlewares/dimensions.js

+/**
+ * Dimensions middleware
+ *
+ * EXAMPLE:
+ * Use it with no parameters to get all the dimensions specified
+ * app.get('/', dimensions(), function(req, res, next){})
+ *
+ * Use it with an array of accepted values
+ * app.get('/', dimensions(['year', 'location']), function(req, res, next){})
+ *
+ * Use it globally
+ * app.use(dimensions())
+ */
+
+function intersect(a, b) {
+    var t
+    if (b.length > a.length) t = b, b = a, a = t
+    return a.filter(function (e) {
+      if (b.indexOf(e) !== -1) return true
+    })
+}
+
+function dimensions(dims) {
+  return function(req, res, next) {
+    if(req.query.dims) {
+      params = req.query.dims.split(",")
+      // If the dims array exists and is not empty
+      if(typeof dims !== 'undefined' && dims.length > 0) {
+        req.dims = intersect(dims, params)
+      } else {
+        req.dims = params
+      }
+    }
+    console.log(req.dims)
+    next()
+  }
+}
+
+module.exports = dimensions