Support widget choice Select/Radios for boolean fields; conditional fields

Select/Radio widget choice:

becomes

Conditional fields.

You can now specify that a group/header/html/input only shows up based on the value of some other field.

In this configuration:

1. Here we say that the html bit "Yes! a cheese lover!" should only show if the value of the field tu_aime_le_fromage_ = 1. That field is a boolean, with 1 meaning Yes.
2. Here we apply the exact same rule, but to a group, thereby turning off multiple fields at once.
3. Another example of showing different messages depending on a field value
4. In this (stupid) example, we only ask for email if the first name is "Rich". We use a case insensitive regular expression, so it works for rich or Rich (etc.).