Expanded the use of the lock mutex already used for loading the player's existing unlock status to guard against races involving the Achievements dialog window reading from data AchievementManager might be in the process of updating. The lock has been exposed publicly and the AchievementsWindow uses it in its UpdateData method, and anywhere else that might modify data used to render that window has also been wrapped with it.
AchievementManager now has a SetUpdateCallback method for providing a single universal callback for anytime something important changes in the achievement state, such as logging in/out, game load/close, or events such as achievement unlocks. AchievementsWindow sets this callback in its own init to its UpdateData method so that the AchievementsWindow gets updated when one of these changes takes place.
This widget is a tab in the AchievementsWindow that displays the player's current achievement progress: which achievements are locked or unlocked, and the progress of achievements that have progress metrics.
This widget displays a header on the AchievementsWindow dialog above the tabs that shows the currently logged in user (if there is one) and the game they are playing (if there is one).
AchievementSettingsWidget is a dialog widget in AchievementsWindow for handling RetroAchievements settings in the user interface. This class contains the physical layout, widget connections, load/save functions and button responses. AchievementsWindow now has a tabbed list that this is inserted into; other tabs will be in a later pull request.
AchievementsWindow is the dialog box that will eventually contain the settings and progress data for RetroAchievements on Dolphin. This adds the barebones dialog, and connects it to MainWindow's MenuBar.
