Add option to generate custom fields for steps

[wtrocki]

Description

Currently rcstep is generating static angular directives for name and email.
We can extend generator to ask what kind of fields are needed and generate them dynamically using

For this issue we should create prototype that will be able to create limited set of types.
For example:

• Text field
• checkbox
• label

To complete this task basing knowledge of yeoman is required: http://yeoman.io.

Ideas

• Allow to consume json file that will specify list of fields and types.
• Ask developer in yeoman generator about steps:

Q: Do you want to add custom fields to the step?
Q: What is your field name
etc.