Custom render support for divider

[MarcoNicolodi]

Hi.

This PR adds support for customizing the "slash" divider.

At our company we'd rather display "1 of 30" instead of "1 / 30".

I also added itemRender tests for simple pagination.

Things to keep aware: I wrapped the slash divider with a <span> with a styleless class for testing purposes. Could it brake production applications?

Also, the first argument of the itemRender is the page number(an integer) , which isnt relevant for the divider. I passed the current page, because if I passed null, it could brake production applications that rely on integer methods without null check.

Thanks.

[coveralls]

Coverage remained the same at 80.693% when pulling a332762ee1a4c33f2a0395b5a71ecf36211c436d on MarcoNicolodi:add-divider-to-itemrender into d78fa4bf319697b228ae889fba003246ded86167 on react-component:master.