change the watch mode of yarn build to use the prepare script
add a --watch flag to prepare script
remove the babel --copy-file flag where possible
remove noise from prepare
improve error reporting from prepare
cleanup
`--declaration true` is always added no matter what app/addon/lib, moved it in `args` array initializer
And add `--emitDeclarationOnly` only is not angular and not storyshots
As of 0.6.0, `downlevel-dts` targets TypeScript 3.4 and there is no option to change that.
So I renamed all the output dirs to `ts3.4` to better represent what's inside them.