Fix aria roles on weekday and month elements

[oigewan]

Fixes: #277

Per https://www.w3.org/TR/wai-aria/roles#columnheader, the columnheader role should go on the equivalent of a <th> element and should be owned by something with the row role.

Also, per https://www.w3.org/TR/wai-aria/roles#rowgroup rowgroup elements should be owned by something with a grid role, so I moved that up as well.

However, this does pose a bit of an issue for people using the weekdayElement prop. Since you're not outputting the result of that in a wrapping div, people passing in an element on that prop will need to be sure to output that role themselves.

Another possible change is for the library to output the wrapping div with the classname and role. I think that would be a breaking change (resulting change in HTML would probably throw off some people's layout CSS), so I'm not attempting that here.

cc: @gpbl

[coveralls]

Coverage remained the same at 100.0% when pulling 09c6604 on oigewan:aria into c9ab28f on gpbl:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 5ca45ce on oigewan:aria into c9ab28f on gpbl:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 36fdfb7 on oigewan:aria into 9fb17f8 on gpbl:master.

[gpbl]

Awesome thanks for your contribution!

However, this does pose a bit of an issue for people using the weekdayElement prop

Sure, however this is left to the developer.

[gpbl]

Published as v5.2.0 🎉