Added accessibility tags into control and removed nested containing div

[Jackleberry]

Added the following tags to the outer div for accessibility:

role="feed"
aria-setsize="-1"
aria-busy={this.state.isInfiniteLoading}

Remove the nested div (smoothScrollingWrapper) and moved infiniteScrollStyles to the outer div.

Fixed lint errors and tests.

[Jackleberry]

@garetht Would you be interested in merging this PR into the main codebase?

[garetht]

@Jackleberry sorry for the delay! This will be a breaking change that is incompatible with older versions so it will have to wait for an explicitly incompatible release.