AVD Creation Dialog unit-test.

Restructure the AVD Creation Dialog to make it testable.
Add a unit-test to cover basic workflow operation.

Change-Id: I9462add74a9bcf96499a9dacacadbcadaee146e1

• sdkmanager/sdkuilib/.classpath[diff]
• sdkmanager/sdkuilib/build.gradle[diff]
• sdkmanager/sdkuilib/src/main/java/com/android/sdkuilib/internal/widgets/AvdCreationDialog.java[diff]
• sdkmanager/sdkuilib/src/main/java/com/android/sdkuilib/internal/widgets/AvdCreationPresenter.java[Added - diff]
• sdkmanager/sdkuilib/src/main/java/com/android/sdkuilib/internal/widgets/AvdCreationSwtView.java[Added - diff]
• sdkmanager/sdkuilib/src/main/java/com/android/sdkuilib/internal/widgets/IMessageBoxLogger.java[Added - diff]
• sdkmanager/sdkuilib/src/main/java/com/android/sdkuilib/internal/widgets/MessageBoxLog.java[diff]
• sdkmanager/sdkuilib/src/main/java/com/android/sdkuilib/ui/GridDialog.java[diff]
• sdkmanager/sdkuilib/src/test/java/com/android/sdkuilib/internal/widgets/AvdCreationDialogTest.java[Added - diff]