Fix Files erroring on download and add editor

[alanzhu0]

Steps to reproduce

• Download a file from the Files app.

Expected behavior

• The file downloads to your computer.

Actual behavior

• An error occurs saying "Connection to application server timed out."

Feature description

• In addition to fixing the error, add an editor to the Files app to allow modifying the files online, if possible.

Rationale for adding feature

• It would be useful to be able to edit files in AFS remotely without going through the command line.

Suggested implementation(s) (if applicable)

• See Director's file editor.