Add warning for large dataset files

[victorlin]

Auspice JSONs can be large, running up to Chrome tab memory limits which shows an error. The effects of this have been mostly mitigated by augur export's automatic minification, however users can still run into the issue if they edit the JSONs outside of Augur. For example, @emmahodcroft ran into the same issue even though she used the --minify-json option because there were other scripts in the workflow to modify branch labels that added back the whitespace.

Related issues

• Firefox working but Chrome displays error 404 for the same URL #1499
• Cannot open 750Mb Auspice JSON in Chrome #1622
• ENH: Warn when exporting large auspice.json, suggest to use --minify-json augur#1155
• export: Automatically minify JSON augur#1331