- remove potential timer in PartBunchBase since it's not used in PartBunch.
  Add timer to AmrObject instead.

- return earlier in "compute-self-field" methods if no solver attached.

- add cpp file for AmrObject class.

modified:   src/Amr/AmrBoxLib.cpp
new file:   src/Amr/AmrObject.cpp
modified:   src/Amr/AmrObject.h
modified:   src/Amr/CMakeLists.txt
modified:   src/Classic/Algorithms/AmrPartBunch.cpp
modified:   src/Classic/Algorithms/PartBunchBase.h