chore: simplify gitignore (#68)

.gitignore

 .idea
 node_modules
 jspm_packages
+npm-debug.*
 link-checker-results.txt
-**/*npm-debug.log.*
-*.js
+app/**/*.js
 *.js.map
 e2e/**/*.js
 e2e/**/*.js.map
 _test-output
 _temp
-
-!karma*.js
-!protractor*.js
-!systemjs.config.js
-!wallaby.js