Fix #2401: Add disabled states for tips & monthly contributions

[kylehickinson]

Summary of Changes

This pull request fixes #2401

Submitter Checklist:

• Unit Tests are updated to cover new or changed functionality
• User-facing strings use NSLocalizableString()

Test Plan:

• Open Rewards Settings
• Verify "View Details" button visible while rewards is enabled
• Verify image + label appear when rewards is disabled

Screenshots:

Reviewer Checklist:

• Issues include necessary QA labels:
  • QA/(Yes|No)
  • release-notes/(include|exclude)
  • bug / enhancement
• Necessary security reviews have taken place.
• Adequate unit test coverage exists to prevent regressions.
• Adequate test plan exists for QA to validate (if applicable).
• Issue is assigned to a milestone (should happen at merge time).

[iccub]

Set milestone before merging