Allow more than one .ne filter in an expression to work as expected

[matburton]

Currently if you have an event expression like example.ne(i,1).ne(i,3) then you may get events returned with i=1 because the second .ne filter overwrites the first

The same applies to metric expressions

Hopefully wrapping all $ne filters in an $and seems like acceptable behaviour even if there's only one?

[Marsup]

I'm resurrecting this PR just to tell I had the same need and implementing $nin was far easier and hopefully more optimized on mongo, hope this helps.