OOUI PHP: Unbreak ButtonWidget

We apparently totally forgot to implement most of the functionality,
and got the rest entirely wrong. Fixing that exposes the fact that
TitledElement is busted too, so fix that as well.

Also tweaked JS ButtonWidget: directly emit the 'click' event
in #onKeyPress rather than calling #onClick.

Change-Id: I4396dc7c592e056ac9b890d5f10f3dd123399c38
build: Introduce 'quick-build' task

Quickly build a no-frills vector LTR version for development.
Submitting as food for thought; is our build too slow?

On my machine it takes eight seconds rather than thirty.

Change-Id: I285e56d5caa152da27535647ab51a32d9d318a58
Merge "build: Introduce 'quick-build' task"
Merge "OOUI PHP: Unbreak ButtonWidget"