Merge pull request #46 from jpfr/master

./configure --enable-multithreading=yes -> MT-Flag
UA_Application and services
use application ptr in the securechannel
Fix multithreading flags in the example servers
move session services
Pointer to Session from SecureChannel
Merge branch 'master' of github.com:acplt/open62541
fix last commit
DateTime_toString and DateTime_toStruct added
resolves "unaccepted policy" client error messages

fixes #44
@uleon it seems that we do not need to sign!