separate bootstrap_form_test.rb into several files

checkbox_test: test relative to checkbox
fields_test: test about generalize response fields
radio_button_test: test relative to radio button
selects_test: test relative to *_select
other_components:
test relative to other components, currently include submit and static-
control

form_test: test about alert, error, help message, and form
form_group_test: test with form_group,
    include those customize form_group or display message in form_group