Added info dialogs for different towers. Made minor UI tweaks, bug fixes, etc.

The main goal for this recent commit was to start to get the game into a
more stable state that is bug-less. It was to also improve user
interaction.

The tower info dialog is added to describe towers to new players. This
commit also added increased control for the back button so that the back
button will dismiss dialogs or active windows instead of just going back
to the menu. Animations has also been added to the gold/lives values to
indicate change whenever it occurs and an alert system has been put in
place to alert players of certain situations (i.e. insufficient funds).