attribute value caching needs a dependency graph

[SmartLayer]

Need the following cases to test the dependency graph generation.

• local-ref to an undefined attribute (therefore its value can only be from a view)
• local-ref to an attribute defined without <origins>
• an attribute defined in a card whose origin is an etheruem:call that has ref=…
• an attribute defined in a token which has an ethereum:call origin that has ref=… to another attribute defined in the token (i.e. not tokenID)
• like the one above, but with a looping reference (which shouldn't be allowed)

Most of these cases also need events.

@James-Sangalli @JamesSmartCell @hboon if you remember an example like that please commend so we can complete the examples.

The goal is to get a portable script (portable = between iOS and Android) that:

Take input: installed TokenScripts.

Output:

1. A list of events to watch for (including the filters)
2. For each of these events, a list of attributes to update (if its value is not already in the event).
3. For each card, the events and attributes relevant to update / retrieve its own attributes

(related work is being done on dependency-graph branch)