Tester: Add ability to clear actions, but keep state intact

[joelwilliamsmith]

It would be useful to be able to reset tester actions, but keep the state intact. This could be an additional flag on the reset function (defaults to true to keep the current API consistent).

e.g.

tester.dispatch({ type: SET_AMOUNT, amount: 100 });

tester.getCalledActions().length; // 1;
tester.getState(); // { amount: 100 }

tester.reset(true, false);

tester.getCalledActions().length; // 0;
tester.getState(); // { amount: 100 }