Add margin to top of form actions

Closes #15213

Also fixes other modal inputs (like add new directory, etc)  

![Screen_Shot_2016-04-20_at_1.47.14_PM](/uploads/14b474da2f86dcc3c1afd9e8ea09e812/Screen_Shot_2016-04-20_at_1.47.14_PM.png)

See merge request !3841