Bugfix for Form->config() field settings

Fixed an issue where if you wanted to set different defaults through
Form->config for different field types (field-checkbox, field-radio)
these settings would be ignored.

These settings are now recognised and if they are not set it defaults
back to just field for its settings as before.
Added isset to $options['type']
Added test case for FormFieldCheckboxWithCustomConfig

Tests for custom configurations with different types of field
Merge pull request #1061 from markwilde/dev

Bugfix for Form->config() field settings