Fixed months for Polish locale

[m-sawicki]

For some reason after upgrading sugar to 2.0 Polish locale for months got mixed up - first and alternative forms switched places. I fixed that plus added proper endings for May (it was broken, so I couldn't use {Month3} for all months).
BTW. The documentation on using alternative/plural forms is really hard to find - I had to look up previous versions of this locale.

[andrewplummer]

Hi... give me a bit and I will look into this. Thanks for helping out here.

[pepkin88]

I think it should stay as it is now. The default should be the genitive case, as it is in v2. In my opinion, people expect date.format('{d} {month} {yyyy}', 'pl') to get properly formatted date, that is '17 lutego 2021', not the improper '17 luty 2021'.
The version 2 is backwards incompatible with 1 anyway, by the semver convention.

As for the missing | for May, yeah, it could be added there.