Feature/complete dataset page styling

[aswallace]

Description

This is a follow-up to #101 , finishing some secondary UX tasks for the datasets page. Closes #119

• Added sorting to dataset manifest table columns & styling to indicate clickable headers
• Added links + styling to reference publication and DOI
• Refactored dataset annotations into their own class, both to standardize them & also to get rid of DatasetColumns.ts (which had gross constants & duplicate code)
• Included a partial fix to the router issue where back button has to be clicked multiple times to go back from app to datasets page, but only works after the first time re-routing. This seems to be somewhat built in to the way react-router pushes history

Not addressed

I have not found a feasible way to make a responsive horizontal overlay on the rows where the hover-state buttons will stick to the right side of the panel when the screen is small (instead of having to scroll right to find them) because of the way the table sets up inheritance. However, this is less urgent, since the same functionality is available when users click on the row to open the side panel

Testing

• Tested on a mock manifest with more datasets since we don't have enough datasets to sort on yet
• Added a couple unit tests

Screenshots

The gray overlay on CREATION DATE is a hover state