Update shinydashboardPage to support latest light "skins".

[hitfuture]

Shinydashboard is based on AdminLTE version 2.38 and needs an update to support the light skin colors. This request includes the changes dashboardPage() parameter skin to support all light skins including blue-light, black-light, red-light, green-light, and yellow-light. An additional change was made to shinydashboard.css to enable the ability to choose the right color for text in the page. I added a test script to show the blue-light skin.

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