lowmem-controller: Split up lowmem-controller feature from lowmem module

lowmem-controller: Split up lowmem-controller feature from lowmem module

The lowmem-controller.c was created by extracting the killing-process
feature from lowmem.c.
    * Newly created: lowmem-controller.c, lowmem-controller.h
    * "lowmem_controller_kill_candidates" function of
      lowmem-controller.c kills procs/apps from candidates list provided
      by the core(lowmem.c).
    * Symbols used only in lowmem-controller.c were moved from lowmem.c
      to lowmem-controller.c.
    * Symbols used both lowmem.c and lowmem-controller.c were moved from
      lowmem.c to lowmem.h.

Change-Id: I8bd0f65acc9df771385c1839096f1283424ce2a5
Signed-off-by: SangYoun Kwak <sy.kwak@samsung.com>