add default value to mapped option of entity
document auto_initialize overriden option
correct overriden option of button and add checkbox overriden option
document overriden options of checkbox
document overriden options of choice field
Merge branch 'overriden_options' of https://github.com/nykopol/symfony-docs into overriden_options

Conflicts:
	reference/forms/types/options/checkbox_compound.rst.inc
	reference/forms/types/options/checkbox_empty_data.rst.inc