Fix TypeError when canceling modal before blurring UserPicker
Change UserPicker to accept a template prop

Clients that don't supply a template prop will still get the old
behavior, the old TEMPLATE value is the default value for the template
prop.
Change UserPicker to accept a dataTextField prop

Older clients that don't supply the prop will still get the old value
from the default prop value.
Change UserPicker to accept a listClass prop

Same drill. Older clients will get the previous behavior by default.
Pass a falsey value to opt out of adding a css class to the UserPicker.