Make heroku friendly

[fembem]

To make this app suitable for deploying to Heroku, I moved package.json to the root directory, as Heroku requires that.

To avoid then having to change a lot of require paths, I moved the contents of the server directory into the root directory as well, which is consistent with common practice. This app uses some server side templates, so can't be split up into a client and a server running on separate machines. Therefore eliminating the server directory has less downside to it.

Gulp and gulp plugin dependencies didn't specify a version, and the newest versions weren't compatible with the gulpfile.js code. The gulp file code doesn't work with version 4, so I set it to version 3, which is contemporaneous to the project code. Gulp version 3 is not compatible with the most recent node versions, so I set the node version to 11.15.0 in package.json. I also set all gulp plugin versions to ones contemporaneous with the project code.

Since Heroku has ephemeral storage, I added the ability to save image files to Mongo. The storage mode is decided at app launch by a config var or by an environment variable. On platforms with both storage options, switching between modes will not make previously uploaded images inaccessible, as the two storage modes use a different file path prefix.

The blog name and Disqus app name have also been extracted into config & environment variables for blog customization.

Lastly, I added an npm build task for the javascript and css assets, which Heroku will run automatically on app deploy.