Fix re-sharing via URL

[melange396]

dont overwrite 'title' with 'customtitle' but use custom in place of title (when available). also, add custom to url-encoded shared links.

[melange396]

To demonstrate the bad/bugged behavior:

1. open https://delphi.cmu.edu/epivis/
2. add a dataset (one from the covidcast indicators endpoint is recommended)
3. hit the "link to this view" button and copy the provided URL to your clipboard
4. open a new tab and paste the url, then hit enter
5. observe the same datasets are displayed (you can also get to this step via the epiportal discovery app)
6. add another dataset
7. again hit the "link to this view" button and copy the provided URL to your clipboard
8. again open a new tab and paste the url, then hit enter
9. observe only the most recent dataset is shown, and the prior ones are gone

To demonstrate the fixed behavior:

• instead of the live version of epivis, open the preview version of epivis for this PR: https://deploy-preview-118--cmu-delphi-epivis.netlify.app/
• follow the other steps
• finally, observe that all signals are shown in the last step

[dmytrotsko]

👍