Add buttons to show passwords wherever they can be entered

Closes #1096

briar-android/src/main/res/layout/activity_change_password.xml

@@ -24,7 +24,8 @@
 			android:layout_height="wrap_content"
 			android:layout_centerHorizontal="true"
 			app:errorEnabled="true"
-			app:hintEnabled="false">
+			app:hintEnabled="false"
+			app:passwordToggleEnabled="true">
 
 			<EditText
 				android:id="@+id/current_password_entry"
@@ -42,7 +43,8 @@
 			android:layout_below="@id/current_password_entry_wrapper"
 			android:layout_centerHorizontal="true"
 			app:errorEnabled="true"
-			app:hintEnabled="false">
+			app:hintEnabled="false"
+			app:passwordToggleEnabled="true">
 
 			<EditText
 				android:id="@+id/new_password_entry"
@@ -60,7 +62,8 @@
 			android:layout_below="@id/new_password_entry_wrapper"
 			android:layout_centerHorizontal="true"
 			app:errorEnabled="true"
-			app:hintEnabled="false">
+			app:hintEnabled="false"
+			app:passwordToggleEnabled="true">
 
 			<EditText
 				android:id="@+id/new_password_confirm"

briar-android/src/main/res/layout/activity_password.xml

@@ -22,7 +22,8 @@
 			android:layout_height="wrap_content"
 			android:layout_centerHorizontal="true"
 			app:errorEnabled="true"
-			app:hintEnabled="false">
+			app:hintEnabled="false"
+			app:passwordToggleEnabled="true">
 
 			<EditText
 				android:id="@+id/edit_password"

briar-android/src/main/res/layout/fragment_setup_password.xml

@@ -26,7 +26,8 @@
 			app:hintEnabled="false"
 			app:layout_constraintLeft_toLeftOf="parent"
 			app:layout_constraintRight_toRightOf="parent"
-			app:layout_constraintTop_toTopOf="parent">
+			app:layout_constraintTop_toTopOf="parent"
+			app:passwordToggleEnabled="true">
 
 			<android.support.design.widget.TextInputEditText
 				android:id="@+id/password_entry"
@@ -62,7 +63,8 @@
 			app:hintEnabled="false"
 			app:layout_constraintLeft_toLeftOf="parent"
 			app:layout_constraintRight_toRightOf="parent"
-			app:layout_constraintTop_toBottomOf="@+id/strength_meter">
+			app:layout_constraintTop_toBottomOf="@+id/strength_meter"
+			app:passwordToggleEnabled="true">
 
 			<android.support.design.widget.TextInputEditText
 				android:id="@+id/password_confirm"