Consistent styling for setup and password activities.

Also removed some unused code from BaseActivity.

briar-android/res/layout/activity_password.xml

@@ -40,7 +40,6 @@
 			    android:imeOptions="actionDone"
 			    android:inputType="textPassword"
 			    android:maxLines="1" />
-
 	    </android.support.design.widget.TextInputLayout>
 
         <Button
@@ -61,7 +60,6 @@
             android:layout_alignTop="@id/btn_sign_in"
             android:layout_alignBottom="@id/btn_sign_in"
             android:layout_centerHorizontal="true"
-            android:gravity="center"
             android:visibility="invisible" />
 
         <TextView