Add proposer slashing detection

[shayzluf]

In order to complete the slasher functionality we need to add proposer slashing functionality to the slasher. in order to complete this functionality we need to complete these tasks:

• write and test proposer slashing detector double proposal detector #5120
• add proposer index to blockheader Align code base to v0.11 #5127
• receive signed blocks from stream and detect slashing Detect Proposer Slashing Implementation #5139
• change proposer slashing to detect by slot and not by epoch spec changes