Move from "test" to "spec" naming convention

[prowwid]

Right now we have *.test.ts and *.spec.ts - we need to rename all of the occurrences of *.test.ts to *.spec.ts

[avchugaev]

It makes sense to rename files to spec.ts.
As for directory structure I see it like this (src directory on top for easier access):

/src
/test
  /api --- test package's public API
  /specs - specifications of package's entities

Currently spec.ts files contains reusable test cases to test against multiple implementation