mdDatepicker: non-default theme has transparent calendar container

[mckenzielong]

Actual behavior:

• What is the issue?
  When using a custom theme that is not named default, the datepicker calendar window is transparent.
• What is the expected behavior?
  The calendar window either adheres to the background palette, or is at least something opaque. Kind of surprised that $element[0].querySelector('.md-datepicker-calendar-pane'); isn't registered with the theming provider. The background styles could work off of this (currently md-calendar and datepicker are registered, but the detached element is the bit that seems to have problems)

CodePen or Steps to reproduce the issue:

• CodePen Demo which shows your issue :
  http://codepen.io/mckenzielong/pen/YWyEqo
• Details:
  Set default theme name to something else (here we have a name 'test'). Click on any of the datepickers to open the calendar window.

Angular Versions:

• Angular Version: 1.5.6
• Angular Material Version: 1.1.0-rc.5

Additional Information:

• Browser Type: Opera/Chrome
• Browser Version: 37/50
• OS: Windows 7
• Stack Traces: N/A

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