Keep an event and link type index

[RuthgerD]

Currently we do not send the link type to the frontend by default, this may limit some use cases.

The reason it is not being send is due to performance requirements, as the types are all strings they would clog the internet tubes needlessly.

To optimize this and to unlock the ability to send over more information in the lean event variant we need an index to map the string types to integer.

2 ways to do this:

1. global RwLock<IndexSet> that is populated when events are inserted into the graph, index is requested through GET
   • pro: complete query-able index
   • con: adds more locking and overhead in hot loop
2. per user IndexSet, populated when events are send over, index is send via socket
   • pro: multi threaded, only indexes events that are requested
   • con: incomplete index, duplicate work with multiple users

once this index is available we can replace the lean event's String usage with u64's.

useful for:
ItJustWorksBetterTM#4