Fixes issue #847 - don't generate a GRUU if the UE doesn't support them
Code review feedback
Merge pull request #848 from Metaswitch/issue847

[Reviewer Alex] Fixes issue #847 - don't generate a GRUU if the UE doesn't support them
Update cpp-common
Add in 3GPP constant
Remove gemini_enabled and memento_enabled options - always enable them
Add submodule updates
Merge pull request #854 from Metaswitch/sto1001

[Reviewer: Alex] Add in 3GPP constant
Take new gemini and memento
Merge remote-tracking branch 'origin/dev' into memento-iss21
Merge pull request #856 from Metaswitch/memento-iss21

[Reviewer: Alex] Remove gemini_enabled and memento_enabled options - always enable them
Merge remote-tracking branch 'origin/dev' into mangelwurzel