experiment audit logs part two: styling and messaging

[danoswaltCL]

placeholder for follow-up fine-tuning work now that experiment audit logs tab is functional and in dev.

styles:

• update the styling to match more closely to the other UI refresh pallette.

• @zackcl mentioned potentially a gray column header in the manner of tables. This is filterable and has columns, but not sortable, and rows are grouped by date, so I don't know if a table header would quite be right, but maybe the point is labels, so maybe we want something like that.

• diff styling

• diff content (currently it's not quite showing the relevant stuff)

• other things?

message content:

• we need to change the language of some of these now that they are experiment-centric.