add typescript support

[agalazis]

I found another generator for the typescript version which is not working by adding ts option here we can ensure its actively maintained

[gautamsi]

you have few options

1. I have created a Yeoman generator generator-keystone-ts long time ago. Updated that today (Jan 19 2019) with latest changes (4.0 release) in original generator as well as fixed many issues related to templates and build systems. try the latest from npm and report any issue there

2. take SydJs-ts repo as starter which I forked from @JedWatson and ported to TypeScript. recently published a branch with upgrade to bootstrap 4 (with scss instead of less).

I voiced for TypeScript long time ago, even ported Beta 7 to TypeScript at https://github.com/gautamsi/keystone-ts. unfortunately Flow was favored over TypeScript by Authors.