Add Android support for a footer close button.

Extending the work done in PR #246 under CB-13409, this adds support to Android for a footer close button similar to the "Done" button on iOS.

The following options are added for Android:

• footer - set to "yes" to show a close button in the footer similar to the iOS "Done" button.
  The close button will appear the same as for the header hence use closebuttoncaption and closebuttoncolor to set its properties.
• footercolor - set to a valid hex color string, for example #00ff00 or #CC00ff00 (#aarrggbb) , and it will change the footer color from default. Only has effect if user has footer set to "yes".

Here are some example screenshots with the relevant options:

location=yes,footer=yes

location=no,footer=yes

location=yes,footer=yes,closebuttoncaption=Done

location=no,footer=yes,closebuttoncaption=Done,closebuttoncolor=#0000ff

location=no,footer=yes,footercolor=#0000ff,closebuttoncaption=Done

location=no,footer=yes,footercolor=#00ff00,closebuttoncaption=Done,closebuttoncolor=#0000ff

location=no,footer=yes,footercolor=#CC000000,closebuttoncaption=Done,closebuttoncolor=#00FFFF