Fix bugs when changing datasets with URL queries defined

[jameshadfield]

Closes #611

Fixed for the colorBy & geoResolution cases.

This maintains the expected behavior when going from http://localhost:4000/local/flu/seasonal/h3n2/ha/6y?c=ep to the 3y dataset.

[trvrb]

@jameshadfield ---

Nice work here. I did catch a small issue:

• Starting from http://localhost:4000/flu/seasonal/h3n2/ha/3y?c=ep if you go to na or go to vic you properly drop the ?c=ep from the URL, but the resulting colorby is wrong in both cases. na gives an LBI coloring and vic gives a region coloring. Both should go to the default coloring by clade.

[jameshadfield]

Starting from http://localhost:4000/flu/seasonal/h3n2/ha/3y?c=ep if you go to na or go to vic you properly drop the ?c=ep from the URL, but the resulting colorby is wrong in both cases. na gives an LBI coloring and vic gives a region coloring. Both should go to the default coloring by clade.

This is now fixed in be70819

[jameshadfield]

P.S. this PR resolves #510

[trvrb]

Thanks for fixing the flu issue. One more bug here @jameshadfield. If I start at http://localhost:4000/flu/seasonal/h3n2/ha/3y?c=lbi and go to "zika" I get an empty URL as expected, however Zika then has date coloring rather than its proper default of country.

[trvrb]

Oh... and another related bug (didn't think about filters until now). If I start at http://localhost:4000/ebola?f_authors=Kugelman_et_al and then go to "zika" I get a full app crash with Uncaught TypeError: Cannot read property 'title' of undefined.

[jameshadfield]

If I start at http://localhost:4000/flu/seasonal/h3n2/ha/3y?c=lbi and go to "zika" I get an empty URL as expected, however Zika then has date coloring rather than its proper default of country.

Fixed in 2cc26d5. I'd forgotten that we use auspice-hardcoded country & geo defaults. If a default is not specified in the JSONs, we now use these instead.

[jameshadfield]

If I start at http://localhost:4000/ebola?f_authors=Kugelman_et_al and then go to "zika" I get a full app crash with Uncaught TypeError: Cannot read property 'title' of undefined.

Should be fixed in 79a3799 but needs testing

[trvrb]

@jameshadfield ---

This is great. I can't find any more bugs. I think this new behavior of preserving state where possible definitely makes the app feel more unified. Please feel free to merge.