Organize components into groups

[nishacodes]

Repos can all remain in the same place, and we can create groups like Polymer does (i.e. core-elements, paper-elements, etc.), whereby all the components can be downloaded in one place. Then we can add the option to the generator-thelma and the user can choose if they want all elements or a specific group.

Suggested groups:

• data-input
• data-transform
• data-visualize

Example: https://github.com/polymer/core-elements