Improve consistency in page titles and menus

In Retention menu and page, accessible to Administrators and Retention Managers, the titles lack some consistency:

• Retention Rules:
  • Shown as "Retention rules" in Retention menu
  • Page title is "RetentionRules", as well as in the browser tab
  • Button to create a Retention Rule in bottom right corner has tooltip "retentionrule"
    
• Retention Search:
  • Shown as "Retention search" in Retention menu
  • Page title is "Retention search" but the browser tab shows "app.title.retentionSearch"
    
• Retention Event:
  • Should probably be "Events" in line with "Retention Rules"
  • Page title in browser tab shows "app.title.retentionEvents"