Remove unnecessary variable in Outline
Half-working adjustable outline font size

Font size and item height are adjusted fine, but all items initially appear as top-level ones (i.e. class members don't appear as such), and some items are displayed incorrectly (e.g. just the class name appears, but no members; moving input cursor into a member in the code inserts that member into the outline; moving to a different one replaces the just inserted previous item; etc.).
Switched to using json for preferences.  No custom vs. default yet
Implemented custom and user json entries
Merge remote-tracking branch 'upstream/master' into sync-outline-font-size-with-editor
Taking default preferences from prefs.json
Fixed alignment for resized ouline items (fonts became clipped)
Some code rearrangements
Merge remote-tracking branch 'origin/master' into sync-outline-font-size-with-editor
Setup temporary prefs json file and classes
fixes to a dart analysis regression
Rewrite "manfest.json" validator to be based on a custom schema definition.
Move non "manifest.json" validation code to "json" directory.
Add ability to validate a json schema is correct.

* Also add support for Boolean values.
Add a few more manifest.json definitions.
Update schema definition of "manifest.json" validator.
Add message id to ErrorCollector.

* This is useful to improving unit tests.
Split lines to fit 80 column.
Add rules for the "sockets" manifest key.
Support more specific validation for "manifest_version".

* Support chaining of base json schema factory with more specific one to enable this specific check.

* Add unit tests.