fix web entities not accepting keyboard focus

[HifiExperiments]

closes #1184

what happened here was:

• EntityItem had a (virtual) method called wantsKeyboardFocus which always returned false
• WebEntityItem had a method called wantsKeyboardFocus that was used as the getter for the property
• RenderableEntityItem also has a (virtual) method called wantsKeyboardFocus which always returned false, which is overridden by RenderableWebEntityItem to return the value it copies from WebEntityItem
• RenderableWebEntityItem performs the copy by calling _wantsKeyboardFocus = entity->wantsKeyboardFocus();
• BUT in Automated entity property serialization #1098, the WebEntityItem getter was sneakily renamed to getWantsKeyboardFocus, so the copy was accidentally always copying false from EntityItem

[ksuprynowicz]

Thank you!