Add additional attributes to choices in ChoiceField

This feature enables user to customize choices in a  drop down
list of a form by adding additional properties to the 'choices'
attribute of ChoiceField class.
Currently, the ChoiceField class has an attribute choices which
takes a list of 2 element tuple by default.
    self.field[<field name>].choices = ([
                                   (option_value1, option_label1),
                                   (option_value2, option_label2)
                                       ])
With this implementation,users can specify an additional transform
function in the forms.fields.SelectWidget class called
transform_html_attrs. Given the option label for a given choice,
transform_html_attrs will return a dictionary containing the html
attributes and their values

Implements: blueprint add-attributes-to-form-field-choices
Change-Id: I8ba997c58b485a33676cf9f350be00a1f365256f
Fixed typos in the QOS Spec forms in Volume Types

Under Admin->Volumes->Volume Types, when we click the 'Create QOS
Spec' button, the Description section mentions 'Manage' instead
of 'Manage Specs'.

Change-Id: Ide4691a79539f2cbf3f94d6f16887eb886f8e23d
Closes-Bug: #1371249
XMLHttpRequest header instantiation for Django-Angular

Change-Id: Ibb6dec29f7f57b9f150578722f7689a34ea20efc
Closes-Bug: #1371718
Updated from global requirements

Change-Id: I827de3494101b0f868fe10bc24c909b8d4477e21
Merge "XMLHttpRequest header instantiation for Django-Angular"
Merge "Fixed typos in the QOS Spec forms in Volume Types"
Merge "Updated from global requirements"
Merge "Add additional attributes to choices in ChoiceField"
Merge branch 'master' of https://github.com/openstack/horizon