Remove sending a list of cookie dicts to CookieManager.add()

[jsfehler]

Adding cookies with a list, eg:

my_list = [{...}, {...}]
CookieManager.add(my_list)

has always been undocumented. Having an argument that takes multiple types seems like a bad idea. If a user really wants to add multiple cookies, it's more likely they're doing:

for c in cookies:
    CookieManager.add(c)

[andrewsmedina]

We should not make break changes without a deprecation warning. So @jsfehler what do you think in 0.15 support the both ways and add a deprecation warning (an example here:

splinter/splinter/driver/webdriver/__init__.py

Line 474 in 2154518

warnings.warn(

) and in the 0.16 we can remove the old way?

[jsfehler]

@andrewsmedina Makes sense to me. See #801