MCOL-987 Add LZ4 compression.

* Adds CompressInterfaceLZ4 which uses LZ4 API for compress/uncompress.
* Adds CMake machinery to search LZ4 on running host.
* All methods which use static data and do not modify any internal data - become `static`,
  so we can use them without creation of the specific object. This is possible, because
  the header specification has not been modified. We still use 2 sections in header, first
  one with file meta data, the second one with pointers for compressed chunks.
* Methods `compress`, `uncompress`, `maxCompressedSize`, `getUncompressedSize` - become
  pure virtual, so we can override them for the other compression algos.
* Adds method `getChunkMagicNumber`, so we can verify chunk magic number
  for each compression algo.
* Renames "s/IDBCompressInterface/CompressInterface/g" according to requirement.

dbcon/mysql/is_columnstore_columns.cpp

@@ -183,6 +183,10 @@ static int is_columnstore_columns_fill(THD* thd, TABLE_LIST* tables, COND* cond)
                     compression_type = "Snappy";
                     break;
 
+                case 3:
+                    compression_type = "LZ4";
+                    break;
+
                 default:
                     compression_type = "Unknown";
                     break;