[Feature request]: Typing Enhancement

Ng2-smart-table is a great component I've been used it for years in some production work loads.
Since then I was think that this package lack some typing for its APIs, I think adding proper types for this package will make using it much easier with angular and typescript.

I hope @akveo open development for the community in order to make it more convenient to the community, if they won't consider it as a priority.