customisable CSS classes, doc passed to template

add {{modalDialogClass}}, {{modalBodyClass}}, {{modalFooterClass}}, {{button.class}}

usage:
```
@showRuleModal = (rule)->
  modalAttrs =
    template: Template.ruleModal
    doc: rule
    title: "Rule #"+rule.index
    modalDialogClass: "rule-modal-dialog"
    modalBodyClass: "rule-modal-body"
    modalFooterClass: "rule-modal-footer"
    buttons:
      delete:
        closeModalOnClick: false
        id: "deleteRule"
        class: "btn-danger pull-left"
        label: "Delete"
      cancel:
        closeModalOnClick: true
        class: "btn-default"
        label: "Cancel"
      save:
        closeModalOnClick: true
        id: "saveRule"
        class: "btn-primary"
        label: "Save"

  if !@ruleModal?
    @ruleModal = ReactiveModal.initDialog(modalAttrs)
    @ruleModal.show()

@hideRuleModal = ->
  if @ruleModal?
    @ruleModal.hide()
```