Add custom branding with icon, brand name and color

[mtrezza]

New Feature / Enhancement Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.

Current Limitation

Currently, Parse Dashboard does not allow to customize the login page and the icon and brand in the top left corner that is visible after login.

Feature / Enhancement Description

Allow to customize icon, brand name and colors.
This issue has been created after PR #1657, which has become stale.

Example Use Case

n/a

Alternatives / Workarounds

n/a

[parse-github-assistant]

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