Increment the CSeq when sending NOTIFYs
Merge pull request #765 from Metaswitch/notify_cseq

[Reviewer: Ellie] Increment the CSeq when sending NOTIFYs
Update memento submodule
Merge pull request #766 from Metaswitch/update_memento

No reviewer required: Update memento submodule
Change Metaswitch submodule refs to ClearwaterCore