Someone using the Binary Clock by their bedside will likely prefer a dimmer screen than a person using it at their office desk. To accomodate both preferences, this commit adds a Settings screen with a slider to adjust the clock's brightness. The settings are accessible only via long pressing on the clock face in order to preserve the minimalist feel of the Binary Clock (a Toast is shown on app launch to inform the user of how to access the settings.) Improves #1 Closes #2