Escape on the new Signature creation modal exits without confirmation

[dspruell-i01]

UI issue with quality of life impact. Hitting Escape key on the new Signature creation modal currently exits the modal without confirmation by user, flushing in progress rule edits and losing work.

It would be better to only allow the modal to be closed with an explicit action (hitting X in the corner, or a close/discard button), and it should have a confirmation dialog to the user.

Reproduce:

1. Navigate to Signatures (/#!/yara_rules)
2. Click Create Signature; Create Signature Artifact modal is rendered
3. Start filling out form fields
4. Hit Escape key while editing in field

This occurs on creation and edit dialogs.