Dashboard CSS keeps disappearing for v0.37

Expected results

Once CSS is written on the Dashboard CSS feature, it should remain persistent.

Actual results

The CSS once applied reflects on the dashboard for the current session. In the subsequent login the CSS script disappears. The number of sessions are arbitrary. Sometimes it happens after one session, sometimes after several.

Screenshots

Before After

How to reproduce the bug

1. Go to Dashboards -> Edit Record -> Scroll to CSS text box
2. Paste some CSS, like

.grid-container{
    margin: 18px;
}
.dashboard-header {
display: none;
}

1. Save and go to Dashboard.
2. You will see the CSS changes. Now log out and log back in, CSS disappears.

Environment

• superset version: 0.37
• python version: 3.6.9

Checklist

Make sure these boxes are checked before submitting your issue - thank you!

• [ Y] I have checked the superset logs for python stacktraces and included it here as text if there are any.
• [ Y] I have reproduced the issue with at least the latest released version of superset.
• [ Y] I have checked the issue tracker for the same issue and I haven’t found one similar.

[willbarrett]

Some members of the community are working on a refactor of the related code, there are a number of related data handling issues. We do not have an ETA for completion or release, but the problem is being actively worked on.

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