re-merge (vuejs-templates#1045)

* Reference dev script in start script instead of copy pasting (vuejs-templates#894)

Less duplication FTW.

* add version tag to config/index.js

* stick to ES5

this file is not transpiled

* Bumping Vue+VueRouter versions, some minor fixes. (vuejs-templates#986)

* switch hello-world tag to PascalCase (vuejs-templates#951)

* fix Es6 code issue.

This file is not transpiled, so we should stick to ES5

* Fix bug in dev-server when a proxyTable entry is a string (vuejs-templates#965)

`options` can not be a `const` because it is modified if value is a string.

* Fix casing

* Revert 9befbfc

* update to vue and vue-router latest version (vuejs-templates#984)

- vue 2.5
- vue-router 3.0

* Fix missing dependency bumps (vuejs-templates#987)

* switch hello-world tag to PascalCase (vuejs-templates#951)

* fix Es6 code issue.

This file is not transpiled, so we should stick to ES5

* Fix bug in dev-server when a proxyTable entry is a string (vuejs-templates#965)

`options` can not be a `const` because it is modified if value is a string.

* Fix casing

* Revert 9befbfc

* update to vue and vue-router latest version (vuejs-templates#984)

- vue 2.5
- vue-router 3.0

* fix missing dependency updates for

* vue-template compiler
* vue-loader

* bump version string

* Fix Unknown plugin istanbul error when no unit test (vuejs-templates#785)

* Fix Unknown plugin istanbul error when no unit test

* simplify handlebars conditionals.

* Revert "Fix Unknown plugin istanbul error when no unit test (vuejs-templates#785)" (vuejs-templates#1035)

This reverts commit 14f2a92.