Insert modal backdrop before modal window in the dom

super simple change. just inserts the modal backdrop if it's in the options before the modal window. this allows the client to set all zindex's to the same value and let the browser's natural stack order them. this helps with stacking modals that are not the same position and size. also added intellij files to the gitignore. 

all tests are passing but let me know if you would like me to write a test to verify that the modal gets inserted after the backdrop in the dom.