Issue #787: Do not create contexts for trivial methods
Issue #787: Do not create contexts for trivial methods

I went with a drastic approach: not creating contexts except if the
method has message sends (this includes inlined JS methods).
More than 30% of the methods are compiled without contexts, speeding up
Amber quite a bit!

- Adds `Node >> requiresSmalltalkContext`
- Do not create contexts for methods without message sends
- Recompiles all js files

amber-smalltalk/amber-contrib-web,amber-smalltalk/amber-contrib-web