LONDON (Reuters) - Chinese commodities group Cedar Holdings has agreed to buy the Stemcor Group, one of the world's biggest steel traders, for an undisclosed sum, Stemcor said on Tuesday.The biggest shareholder of London-based Stemcor is U.S. private equity group Apollo Global Management . Cedar and Stemcor aim to finalise the deal in the first half of 2020, a statement said."Stemcor has a well-established global sales network, which will offer potential synergies with the existing domestic and..