Release notes for 0.23.x Release 4 /w Chromium 68

[kjozwiak]

Release Notes:

• Min browsing activity message is retained even after min criteria is met. (#14767)
• Favicon.js fails with cross origin href due to lacking required attribute (security). (#14742)
• [hackerone] local files. (#14642)
• Tor process remains alive after crash. (#14636)
• Disable "Always ask me where to save files" still ask user and open Save As dialogue. (#14625)
• Stats ref codes should not be sent at startup. (#14615)
• Crash about dom storage context while browsing Twitter in private tabs with Tor. (#14392)
• Extension popups empty and transparent on first click after Brave restart. (#13633)
• URL ending with .pdf causes Brave to ignore Content-Type, then fail because document is not PDF. (#10554)
• Update to Chromium 68.0.3440.75. (#14886)
• Update Muon to 8.0.3. (#14885)