Prevent default on all key events when enabled (alwaysPreventDefault opt)

kb-controls used to preventDefault on all keys, before
https://github.com/chrisdickinson/kb-controls/pull/2 - we relied on this
to prevent game controls keys from unintentionally interfering with UI
elements. Adds alwaysPreventDefault option to disable this behavior if
undesired. Fixes holding Tab (for voxel-sprint) cycling through
voxel-debug datgui kb-bindings-ui binding widgets, and also
voxel-console '.' or '/' opening with doubled '..' or '//'.
0.2.0