string utils: remove to_string

src/account.cpp

src/call.cpp

src/client/videomanager.cpp

src/jamidht/jamiaccount.cpp

src/jamidht/namedirectory.cpp

src/manager.cpp

src/media/media_codec.cpp

src/media/media_encoder.cpp

src/media/video/video_device.h

src/media/video/video_rtp_session.cpp

src/preferences.cpp

src/sip/sdp.cpp

src/sip/sipaccount.cpp

src/sip/sipaccountbase.cpp

src/sip/sipcall.cpp

src/sip/sipvoiplink.cpp

src/smartools.cpp

src/string_utils.h

src/upnp/upnp_context.cpp

src/upnp/upnp_igd.h