[build] Add CMake Build System

  - remove key storage stuff
  - fix daemon build under osx with cmake
  - Set SOVERSION of libseafile to 0
  - remove shared library version
  - python support
[common] use packed attribute if available
[cleanup] silence multiple compiler warnings

  - silence the warning of uninitialized head_id in putcommit-v2-proc.c
  - silence the warning of implicit declaration of g_open in test-seafile-fmt.c
  - silence the warning of implicit declaration of g_stat in test-cdc.c
  - silence the warning of uninitialized e in merge-recursive.c
  - silence the warning of bm->size >= 0 is always true in fileserver.c
[build] cmake patch for new-sync
[build] more cmake fixes for new-sync
[build] remove avl in cmake build system
[common] cleanup avl and related code
[common] remove unused functions

 - seaf_repo_manager_get_repo_prefix
 - seaf_repo_manager_repo_exists_prefix
[client] land new changes of new-sync for osx
[build] fix bus error while execute make -jN (N>1)

  - please use latest version of seaf-codegen.py,
     at least the one in haiwen/libsearpc#17