Our current convention is to treat abbreviations longer than 2
characters as regular words and capitalize only the first character.

We already use "Json" form across the codebase instead of "JSON".

This commit applies the same convention to the JSON Schema type
introduced by the recent commit e9e6b12.

Modify our build system to support two targets again:
 - ES2017 for Node.js 8.x LTS
 - ES2018 for Node.js 10.x, which is going to enter LTS in Oct 2018

While I was adding the new build target, I cleaned up our infrastructure
to make it easier to add/remove build targets in the future.

 - Dist folders are always versioned using Node.js major version number,
   i.e. `dist8` for Node.js 8.x and `dist10` for Node.js 10.x

 - All package.json references to `dist` were replaced with `dist*`

 - "files" section in package.json file were simplified by leveraging
   wildcards.

While I was making these changes, I also fixed several places in various
package.json files that were not consistent with the rest of the
monorepo.

Extract code dealing with Node.js versions and different `dist` folders
from packages' `index.js` files into a shared `@loopback/dist-util`
package.

 - @loopback/authentication@0.9.0
 - @loopback/boot@0.9.0
 - @loopback/build@0.6.1
 - @loopback/cli@0.10.0
 - @loopback/context@0.9.0
 - @loopback/core@0.7.0
 - @loopback/dist-util@0.2.0
 - @loopback/metadata@0.7.0
 - @loopback/openapi-spec-builder@0.6.0
 - @loopback/openapi-v3-types@0.6.0
 - @loopback/openapi-v3@0.9.0
 - @loopback/repository-json-schema@0.8.0
 - @loopback/repository@0.9.0
 - @loopback/rest@0.9.0
 - @loopback/service-proxy-proxy@0.3.0
 - @loopback/testlab@0.9.0
 - @loopback/example-hello-world@0.6.0
 - @loopback/example-log-extension@0.8.0
 - @loopback/example-rpc-server@0.6.0
 - @loopback/example-todo@0.8.0
 - @loopback/docs@0.6.0

 - @loopback/authentication@0.10.0
 - @loopback/boot@0.10.0
 - @loopback/build@0.6.2
 - @loopback/cli@0.11.0
 - @loopback/context@0.10.0
 - @loopback/core@0.8.0
 - @loopback/dist-util@0.3.0
 - @loopback/metadata@0.8.0
 - @loopback/openapi-spec-builder@0.7.0
 - @loopback/openapi-v3-types@0.7.0
 - @loopback/openapi-v3@0.10.0
 - @loopback/repository-json-schema@0.9.0
 - @loopback/repository@0.10.0
 - @loopback/rest@0.10.0
 - @loopback/service-proxy-proxy@0.4.0
 - @loopback/testlab@0.10.0
 - @loopback/example-hello-world@0.7.0
 - @loopback/example-log-extension@0.9.0
 - @loopback/example-rpc-server@0.7.0
 - @loopback/example-todo@0.9.0
 - @loopback/docs@0.7.0