Helios references browser changes:

- adds Find Class command
- adds Browse method command
Fixes HLFindReferencesCommand when a Metaclass is selected
Better fonts for line numbers in CodeMirror
helios: adds focus shadow around buttons
Merge pull request #828 from herby/extensions-ordered

Fixes shuffling extension methods part of st and js exports.
Merge branch 'master' of github.com:amber-smalltalk/amber
re-commit all packages after changes in commit e18a70f
Merge pull request #827 from herby/newvalue-refactor

Newvalue refactor
Formatting helios.less
Making themes customizable

Legacy IDE as well as Helios look for
`Smalltalk vm at: 'codeMirrorTheme'` before setting their defaults.

Helios defaults are 'default helios', legacy IDE defaults are 'default'.
Extracting Helios fonts and colours.

Helios's colour and fonts settings are in CodeMirror helios theme.
Hint selection menu should have sans-serif menu font.

IMO. I'm not going to fight for this.