Allow for multiline snackbar messages

[steinbergh]

Currently SnackBar notifications are expected to be a very specific height causing SnackBars with multiline messages to stack on top of each other, I would like for variable heights to be accounted for or would like to have access to the TransitionProps and level prop of the SnackBarItem to customize this.

[iamhosseindhv]

I got your point. This is a must have and something that notistack has to manage internally. I'll plan for adding this to the next version.

[iamhosseindhv]

@steinbergh Fix for this is pushed to the master and will be published in the next version. see changelog for more info.

[steinbergh]

Thanks so much!

[iamhosseindhv]

@steinbergh This is published now.