* WIP add instanbul code coverage to vue files
* move webpack coverage config to a separate file for test:coverage, pin dependencies, remove istanbul-instrumenter-loader
* dont include node_modules in babel config, it breaks istanbul for some reason
* ignore spec files from coverage
* document coverage files, remove unused karma config
* use test instead of test:coverage in config.yml, disable code and link to issue to enable coverage in Vue <template>s
