add me function pointers for screen contents
Fix QP<18 dequant UT bug at encoder side
This should be UT for QP<12.
Merge pull request #831 from sijchen/md_merge144

[Encoder ME] Add ME function assignment for Screen Content Coding
Merge pull request #853 from dongzha/FixEncUTDequantBugMaster

Fix encoder dequant Unit Test bug for master