Headers may not be properly processed

Problem/Motivation

• Headers aren't being included in the request
• The input box is a single line which doesn't allow me to submit multiple headers
• Using '\r\n' may not work cross-platform

Steps to reproduce

1. Add a rule for Request HTTP data
2. See that you can't add more than one line in the Headers input box
3. Add a header
4. Make a request
5. The header isn't added

Proposed resolution

• Change the input box for Headers to be multi-line
• Check if the $headers is already an array before exploding
• Change the explode to use only '\n' and then trim the values to remove any '\r' characters

Remaining tasks

• Submit a patch

User interface changes

• Headers input box is changed to multi-line input

API changes

• n/a

Data model changes

• n/a