Better error handling for the event binding parser

[d3lm]

Currently the event parser's error handling is kept to a minimum, meaning if the parser fails to parse a template stream binding, it will gracefully fail and not transform the binding at all. This obviously has an impact on the developer experience, beacuse the parser doesn't produce meaningful error messages at build time. For example the parser could produce error proper messages for the individual parts of the DSL, such as

• event name
• stream name
• payload