Hackathon submission state buttons are visually confusing

[garyhtou]

The admin hackathon show page contains buttons to transition the state of a hackathon submission (Approve, Reject, and Hold for Review). It's a bit confusing because all the buttons appear at once (similar to #401)

We should hide certain buttons depending on the current state. For example, approve -> approve should not be a valid state transition; thus, we should hide the approve button if the current state is approved.

---
title: Hackathon Submission State Diagram
---
stateDiagram-v2
    [*] --> Pending
    Pending --> Approved
    Pending --> Rejected
    Approved --> Pending: Hold for Review
    Rejected --> Pending: Hold for Review

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[northeastprince]

Those buttons should be disabled, but they're not showing up visually for some reason.