Adds box-shadow to `#searchbox` when either `#search_query` or any
of the pills have focus. Uses jquery instead of pure css as the
`:focus` event occurs on `#search_query`, while we want to add
box-shadow to `#searchbox`. This could have been done with
`:focus-within` CSS selector, but it is not supported in IE or Opera.
`#search_query` already had an onfocus/focusout listener, adding
listeners to `#searchbox.pills` for those events wouldn't have worked
as you don't want the focusout event to fire when the focus shifts
from input to pill.
Also adds `focusin`, `focusout` and `css()` to zjquery. `css` is
same as `val`, except it returns an empty object in case of no value
instead of an empty string. I don't think `css()` is valid syntax
in actual jquery.