* Implement data source templates
* Remove optional param from wasm instantiate
* Add all types for solidity to typescript mapping
* Set contract address in context for data source templates
* Implement block handlers for data source templates
* Handle BigNumber event params in watchers
* Customize decimal according to limits of IEEE-754 decimal128
* Add definition for custom scalar BigDecimal
* Invoke handlers based on watcher-ts events
* Read subgraph yaml and listen to events from watcher-ts
* Create GraphWatcher class to use in generated example contract watcher
* Call graph-node event handler from generated watcher