Parsing and emit for computed properties

This is based on the plan in issue #1082. The type checker support, .d.ts generation and language service support (other than navigation items). I plan to work on the type system side next.
Extremely subjective, but, I'd rather this be 

`symbol.valueDeclaration !== node || hasUnknownComputedName(node)`

just because it's easier for me to focus on the common case at hand.