Make form checking design consistent

[ibeckermayer]

Currently, for the Change Password Modal (the one that pops up when you click "Change Password" on the Settings page) has a grayed out, disabled button when the form is invalid. On the other hand, the other modals don't have the grayed out buttons. Let's make this consistent.

I think we should always allow the user to press the button, and then pop up the error messages on form submit, if they failed to fill out the form correctly. With the grayed out option, we always need to show the user the error message while they're typing (so that they understand why the button is grayed out), which is semantically false (there's not actually an error yet, they're just in the process of typing).