Merge @thomasyu888's updates to use Golem for Shiny app structure

[jaeddy]

This PR merges Tom's various changes to repo structure to conform with a standard Golem-based Shiny app, including some additional functionality for handling Synapse login.

[thomasyu888]

Testing this branch: this might be somewhat cumbersome to set up initially, but i think would be easier to adapt/extend moving forward (and you could probably get it working a lot more quickly than me anyway):

1. There are 3 files and instructions for how to validate/upload manifests here; along with another for publications attached
2. if you were to subset those (maybe not the additional_standard_terms sheet...), then do a Synapse tableQuery to grab the matching rows from the Publications, Datasets, and Tools and pull the CSVs/dfs
3. ideally, there should be a way to run a test for each of the manifest files without needing to use the app itself or upload the final results to Synapse (e.g., my comparing the ready-to-upload data to the CSV/df rows)
4. if everything matches, then you at least know that the tool is still working the same after your changes
5. if they don't match, then we'd need to take a closer look... in case you actually fixed a bug somewhere

[jaeddy]

Thanks, @thomasyu888! I'll copy this to an issue for reference.