nested many form not work in modal

[fmh]

this issue is just in modal
before click to add nested form (nested many)

after click

it is caused by something that removes .btn-group content

[fmh]

it is caused by this lines:

https://github.com/sferik/rails_admin/blob/v0.0.1/app/assets/javascripts/rails_admin/ra.widgets.coffee#L43

https://github.com/sferik/rails_admin/blob/v0.0.1/app/assets/javascripts/rails_admin/ra.widgets.coffee#L52

[fmh]

@mshibuya : maybe a fix (it work for me)

$(this).siblings('.btn').remove()