Initial pass on the design documentation.

The design doc and software design doc.
The UML images are generated with plantUML from the *.puml files.

docs/uml/tasks.puml

@@ -0,0 +1,13 @@
+@startuml
+skinparam componentStyle rectangle
+[Tasks] --> [Switcher]
+[Tasks] --> [Display]
+
+package "Button Listeners" {
+   [Tasks] --> [A Button Listener]
+   [Tasks] --> [B Button Listener]
+   [Tasks] --> [Start Button Listener]
+}
+
+@enduml
+