Update tables to use dark theme

- Set auth cell fields to system color
- Update Swift-flow main storyboard to use system colors

Author: cbess

Auth/FirebaseAuthUI/FUIAuthTableViewCell.m

@@ -18,6 +18,15 @@
 
 @implementation FUIAuthTableViewCell
 
+- (void)awakeFromNib {
+  [super awakeFromNib];
+  
+  if (@available(iOS 13.0, *)) {
+    self.textField.textColor = [UIColor labelColor];
+    self.label.textColor = [UIColor labelColor];
+  }
+}
+
 - (void)setLabel:(UILabel *)label {
   _label = label;
   [self layoutIfNeeded];

EmailAuth/FirebaseEmailAuthUI/FUIPasswordRecoveryViewController.m

@@ -94,6 +94,11 @@ - (void)viewDidLoad {
   self.navigationItem.rightBarButtonItem = sendButtonItem;
 
   [self enableDynamicCellHeightForTableView:_tableView];
+  
+  if (@available(iOS 13.0, *)) {
+    _tableView.backgroundColor = [UIColor systemBackgroundColor];
+    self.footerTextView.textColor = [UIColor secondaryLabelColor];
+  }
 }
 
 - (void)viewDidLayoutSubviews {

EmailAuth/FirebaseEmailAuthUI/FUIPasswordSignInViewController.m

@@ -111,6 +111,10 @@ - (void)viewDidLoad {
   [_termsOfServiceView useFooterMessage];
 
   [self enableDynamicCellHeightForTableView:_tableView];
+  
+  if (@available(iOS 13.0, *)) {
+    _tableView.backgroundColor = [UIColor systemBackgroundColor];
+  }
 }
 
 - (void)viewWillAppear:(BOOL)animated {

EmailAuth/FirebaseEmailAuthUI/FUIPasswordSignUpViewController.m

@@ -127,6 +127,10 @@ - (void)viewDidLoad {
   self.navigationItem.rightBarButtonItem = saveButtonItem;
 
   [self enableDynamicCellHeightForTableView:_tableView];
+  
+  if (@available(iOS 13.0, *)) {
+    _tableView.backgroundColor = [UIColor systemBackgroundColor];
+  }
 }
 
 - (void)viewDidLayoutSubviews {