Execute unit tests in 'web' subproject

[krzema12]

See e.g. https://blog.kotlin-academy.com/testing-common-modules-66b39d641617 (close to minimal config: https://github.com/MarcinMoskala/KotlinAcademyApp/blob/cc090bb5acaa7e26fc26952a4c6b6290e5612c5c/common-client-js/build.gradle).

[krzema12]

Maybe the core project should be self-contained and execute tests for JVM and JS?

[krzema12]

See fsynth/web/build/classes/kotlin/test/web_test.js - it checks whether kotlin is defined and it's not, and fails on kotlin being undefined.

[krzema12]

Kotlin 1.3 introduces some changes in how multiplatform projects are configured. This issue may no longer exist after migration to 1.3.

[krzema12]

I have something working already: https://github.com/krzema12/fsynth/tree/wip-fixing-js-unit-tests

I made several changes, so left to do:

• check which change(s) was/were essential and clean up the code
• fix Karma config to work also for other absolute paths of the project (e.g. Travis CI)
• make sure that Chrome/Chromium can be downloaded by the build script itself

[krzema12]

If this pull request Kotlin/kotlin-frontend-plugin#101 gets accepted, it can be done in a cleaner way. See the comment inside karma.conf.js for details.