Update default for magic titlebar on Windows/Linux; add favicon for about:autofill + about:passwords

Auditors: @BradRichter, @darkdh

Fixes #5416 (URL bar duplicates the title bar)

1. Install Brave (fresh install or move session folder) on Linux
2. Launch Brave and visit brave.com
3. URL bar should always be showing
4. Go to about:preferences and ensure "Always show URL bar" is enabled

1. Install Brave (fresh install or move session folder) on Windows
2. Launch Brave and visit brave.com
3. URL bar should be hidden unless mouse is in there
4. Go to about:preferences and ensure "Always show URL bar" is disabled

Fixes #5398 (about:autofill missing Brave favicon)

1. Launch Brave and visit about:about
2. Click about:passwords and notice the favicon now shows up
3. Click about:autofill and notice the favicon now shows up

Author: bsclifton

app/extensions/brave/about-autofill.html

@@ -8,6 +8,7 @@
     <meta name="availableLanguages" content="">
     <meta name="defaultLanguage" content="en-US">
     <meta name='theme-color' content='#ff5000'>
+    <link rel="shortcut icon"type="image/x-icon" href="data:image/x-icon;,">
     <title data-l10n-id="autofillTitle"></title>
     <script src='js/about.js'></script>
     <script src="ext/l20n.min.js" async></script>

app/extensions/brave/about-passwords.html

@@ -8,6 +8,7 @@
     <meta name="availableLanguages" content="">
     <meta name="defaultLanguage" content="en-US">
     <meta name='theme-color' content='#ff5000'>
+    <link rel="shortcut icon"type="image/x-icon" href="data:image/x-icon;,">
     <title data-l10n-id="passwordsTitle"></title>
     <script src='js/about.js'></script>
     <script src="ext/l20n.min.js" async></script>

js/constants/appConfig.js

@@ -133,7 +133,7 @@ module.exports = {
     'security.passwords.dashlane-enabled': false,
     'security.passwords.last-pass-enabled': false,
     'general.downloads.default-save-path': null,
-    'general.disable-title-mode': process.platform === 'win32',
+    'general.disable-title-mode': process.platform === 'linux',
     'advanced.hardware-acceleration-enabled': true,
     'advanced.default-zoom-level': null,
     'advanced.pdfjs-enabled': true,