Merge branch 'mannol1-master'
Core should no longer attempt to send data faster than the links can
carry it.
Const correctness for toxcore/Messenger.c and related files
Const-correctness for toxcore/net_crypto.c
Const-correctness for toxcore/onion_announce.c
Const-correctness for onion.c
Const-correctness for onion_client.c
Fixed video in call sometimes freezing.

This should not happen anymore.
Const-correctness for TCP_client.c
Const-correctness for TCP_server.c
Const-correctness for tox.c
Updated some items in the TODO list.
Merge branch 'const_correctness' of https://github.com/schuetzm/ProjectTox-Core
Fixed const related warnings.
Resolved conflicts when merging upstream