Split LArray into Java-based projects and Scala API

This change set includes the following major changes:
 * Project structure is now larray-buffer (java) <- larray-mmap (java + JNI) <- larray (scala/java API)
 * Off-heap memory is implemented as LBuffer
 * Translate off-heap memory allocator and off-heap/mmap buffer from Scala to Java
 * Provides int-indexed accessor that improves the performance for LArray with less than 2G entries.