Updates CodeMirror to version 3.20
- use support/codemirror.js to load CodeMirror
- removes custom amber support (in favor of the default smalltalk mode)
- updates IDEs to reflect codemirror changes
Simplifies Package >> classes
Fixes issue #792

- Moves comparison methods to ProtoObject
- Adds `#=` to JSObjectProxy
- Adds comparison tests to JSObjectProxyTest
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
more cleanup for `asSet` usages
Fixes issue #752

- Introduce a common `Service` class, superclass of `Transcript` and co.
- Fix service registration in Helios, IDE and Kernel
- Explicitely load Helios in helios.html