Unchecks some registration fields by default.

Adds a key labeled `checked` with a value of `false` to some of the registration
fields so they are not checked by default in the settings form. Specific
fields, per comment by @amandafrench:

* Technology skill level.
* T-shirt size
* Children

Fixes #62.
Merge pull request #65 from clioweb/uncheck-fields-default

Unchecks some registration fields by default.