Module creation

1. pjsua2 wapper code moved to pjsua2 module
2. sip module created
    a- it has a child module sip-contracts, it currently contains wrapper objects over the pjsua2 API objects
    b- dependent on pjsua2 module
    c- other wrapper code over pjsua2 APIs will be added here, To be done
Module creation

1. Code added to core sip module
2. Logging module created
3. utils module created, currently added executors to this module itself, to be added as a separate module of its own
4. Commented some uses of SIPSDK and Context module in "sip" module