refactor(scope): separate controller from scope

Controller is standalone object, created using "new" operator, not messed up with scope anymore.
Instead, related scope is injected as $scope.

See design proposal: https://docs.google.com/document/pub?id=1SsgVj17ec6tnZEX3ugsvg0rVVR11wTso5Md-RdEmC0k

Closes #321
Closes #425

Breaks controller methods are not exported to scope automatically
Breaks Scope#$new() does not take controller as argument anymore

docs/content/guide/dev_guide.expressions.ngdoc

@@ -51,14 +51,14 @@ You can try evaluating different expressions here:
 <doc:example>
 <doc:source>
  <script>
-   function Cntl2() {
-     this.exprs = [];
-     this.expr = '3*10|currency';
-     this.addExp = function(expr) {
+   function Cntl2($scope) {
+     $scope.exprs = [];
+     $scope.expr = '3*10|currency';
+     $scope.addExp = function(expr) {
         this.exprs.push(expr);
      };
 
-     this.removeExp = function(contact) {
+     $scope.removeExp = function(contact) {
        for ( var i = 0, ii = this.exprs.length; i < ii; i++) {
          if (contact === this.exprs[i]) {
            this.exprs.splice(i, 1);
@@ -101,10 +101,10 @@ the global state (a common source of subtle bugs).
 <doc:example>
 <doc:source>
  <script>
-   function Cntl1($window){
-     this.name = 'World';
+   function Cntl1($window, $scope){
+     $scope.name = 'World';
 
-     this.greet = function() {
+     $scope.greet = function() {
        ($window.mockWindow || $window).alert('Hello ' + this.name);
      }
    }