#a11y

In this commit we can simply replace the role to menu and the sub div's role to menuitem if we want the multiselect filter to behave like the other filters but the problem is that it focuses on the whole div instead of the checkbox.I am pushing the changes with the above suggestions but someone testing this might switch to prior commit to see another version of this MR.

Re #23
With voiceover switched on now all the things mentioned are resolved except 5 which i am not sure whether we want to do that as the 2 elements are different in nature.
I have tested everything else on Safari and chrome and it works fine in these two browsers.It would be helpful if you can have a look at this once again @rkoller and verify the changes.
Marking it NR.

There will be more a11y fixes coming, but I aim to try to keep them as small and narrowly scoped as possible.