feat(tasklist/forms): allow form scripts

Add ability to execute custom javascript in the scope of a form.

- The script must be contained in a script tag such as
  <script form-script type="text/form-script"></script>

- Inside the script, two variables are present:

  $scope
    - the current scope to which the script may bind to

  inject: a function that may be used to inject and use angular
    - services. To use inject, a user must call the function with a
      callback definition that either is a function which declares
      a $inject field or an array such as
      [ '$dep1', '$dep2', function($dep1, $dep2) {}].

Example:

  <script form-script type="text/form-script">

    // may use $scope to bind against the current scope directly
    // or use #inject (see below) to obtain application services

    inject([ '$scope', '$http', function($scope, $http) {

	  // $http service may be used
      $scope.$watch('variablesForm.$valid', function(newValue) {
        console.log('Form', newValue ? 'valid' : 'invalid');
      });
    }]);
  </script>

Closes CAM-1322
Merge branch 'master' of github.com:camunda/camunda-bpm-platform