Add header name
Add custom header type and related functions
Unit test utility functions
Set Session-Expiry to configured value
Fix up UT infrastructure
Add UT of header addition
Add init.d function
Markups
Merge pull request #423 from Metaswitch/session-expires

Reviewer Mike - Session expires
Fix failing UT thanks to mis-markup
Merge pull request #424 from Metaswitch/session-expires

No review required - Fix failing UT thanks to mis-markup