Upgrading to jQuery 2.0.3.
Changing the storage for context names to data- attributes.

This seems like a more proper way of storing the values than in ID
attributes.
Showing and hiding space contexts depending on children visibility.

When a space context has none children visible, due to a time-context
display filter, it will now be hidden as well. When children reappear, the
whole space context will show again as well.

This is neither clean nor optimal yet.
Removing a space context after last child is completed.

When a space context doesn't have any more children, after the last one is
completed, there's no use of showing it anymore. It's removed now from the
DOM.
Adding missing field declaration.

This was causing a NOTICE type error of declaration missing.
Hiding the context button when context is removed.

When the context is empty and thus removed from list, there's no point in
keeping the button for it. It's removed now as well.
Optimizing search for first parent.

The closest() function is quicker than filtering all parents.
Further optimizations in parent search.
Optimizing context cleanup after item completion.

Traversal will now only search through the siblings and parents of the
immediately completed item.
Further optimizations to parent search.

All parents(:first) calls were replaced with closest() which in all these
cases should produce a match quicker and with less memory used.
Disabling the context button when hiding context.

When the context is hidden, because all of its children are hidden, the
corresponding button for that context is now set to 'off' status.
Merge branch '10-hide-empty-sections'