Update cpp-common
Update PJSIP
Merge pull request #15 from Metaswitch/update_pjsip

[No review] Update PJSIP
Update cpp common
Merge pull request #16 from Metaswitch/update_cppcommon

no reviewer: Update cpp common
Add -fPIC to the compile command
Merge pull request #17 from Metaswitch/position-independent-compiles

No review required - Add -fPIC to the compile command
Change Metaswitch submodule refs to ClearwaterCore