Improvements to feedback comments mailer

[mvl22]

1. Please set a Reply-To, set to the e-mail given by the user, to make replying easier.

2. The layout of the e-mail is missing line breaks. It comes through as follows:

Comment with: Name Jane Smith Email: foo@example.com URL: https://camcycle.cyclescape.org/overview Body: Test feedback

3. The subject line needs to have the feedback number in it, for easier referencing.

[mvl22]

Given the amount of spam coming through this at the moment, it would be good to make these quick fixes (which are presumably very simple), to make it easier to parse the e-mail visually.

[nikolai-b]

@mvl22 should we add a custom form element to reduce spam e.g. in words how many wheels does a bicycle have?

[mvl22]

Yes, could try that.