Move app locking logic into dedicatd LockManager

.../org/briarproject/bramble/api/account/AccountManager.java

.../org/briarproject/bramble/account/AccountManagerImpl.java

...org/briarproject/bramble/account/BriarAccountManager.java

...java/org/briarproject/briar/android/AndroidComponent.java

...project/briar/android/AndroidNotificationManagerImpl.java

...c/main/java/org/briarproject/briar/android/AppModule.java

...g/briarproject/briar/android/account/LockManagerImpl.java

...rg/briarproject/briar/android/activity/BriarActivity.java

...riarproject/briar/android/controller/BriarController.java

...project/briar/android/controller/BriarControllerImpl.java

.../org/briarproject/briar/android/login/UnlockActivity.java

...iarproject/briar/android/navdrawer/NavDrawerActivity.java

...rproject/briar/android/navdrawer/NavDrawerController.java

...ject/briar/android/navdrawer/NavDrawerControllerImpl.java

...briarproject/briar/android/settings/SettingsFragment.java

...iarproject/briar/android/splash/SplashScreenActivity.java

...ain/java/org/briarproject/briar/android/util/UiUtils.java

.../java/org/briarproject/briar/api/android/LockManager.java