Merge pull request #366 from colorant/yarn-dev

More yarn code refactor

Try to retrive common code in yarn alpha/stable for  client and workerRunnable to reduce duplicated codes. By put them into a trait in common dir and extends with them.

Same works could be done for the remaining files in alpha/stable , while the remainning files have much more overlapping codes with different API call here and there within functions, and will need much more close review , aslo it might divide functions into too small trifle ones, thus might not deserve to be done in this way.

So just make it run for these two files firstly.