…riants (source-academy#1052)

* Add a default variant as a constant

* slangHelper: Add variant as a parameter to createContext

* Use default source variant when creating default workspace

* Use default variant when clearing context

* Fix style issues

* Support non-deterministic Source (#1)

* add support for non-deterministic Source

* update notification to show correct chapter name

* Set variant property in createContext

* Handle variant independently from chapter

* clear context when variant changes

* make variant optional in createContext

* use function for calling non-det

* add semicolon

* remove shadowed name

* generalize chapter selection

* fix test

* handle variant urls

* format

* add space for variant display

* change variable name

* remove variant export

* rename datastructure

* use variant in button name

* use default variant value

* fix: chapter in share link

* refactor language url name

Co-authored-by: Arsalan Cheema <arsalanc.v2@gmail.com>
Co-authored-by: martin-henz <henz@comp.nus.edu.sg>