This fixes two bugs:
1. When setting a value the "previousValue" for determining when to fire change events isn't updated.
2. When pressing 0 in an empty number field, it shouldn't fire a change event because it didn't change.
Emit "change" events when clicking number spinner (bug https://github.com/powmedia/backbone-forms/issues/214)
Allow negative sign, which is part of a valid number.
Removed redundant question mark.
Update distributions.