Squashed 'extern/leveldb/' content from commit 2c9a52f

git-subtree-dir: extern/leveldb
git-subtree-split: 2c9a52fa4c0385d148d191589bd7b2c717bb500f
Merge commit '3627a20dc9829385a3d33617665dc81b94024f36' as 'extern/leveldb'
Move leveldb files to extern and unity dirs