Editable single IA Page

//cc @jbarrett @jdorweiler @russellholt 
Created a separate endpoint and page for editing: /ia/edit/<id>, and another endpoint for saving the edited data.

IAPageEdit.js has a save button which is disabled unless some field's text changes (I'm using the keydown event).
Clicking on the save button, if active, sends a POST request to ia/save, which updates the database with the new data for that IA (thanks @jbarrett for this) and returns to IAPageEdit.js.
If the POST request and the update went well, IAPageEdit.js will redirect to /ia/view/<id>, as discussed with @russellholt.
I see it too, it's the $_ in the error message which is undefined, but the catch block isn't actually being executed.