tracker: add start/stop tracking apis for internal usages

tracker: add start/stop tracking apis for internal usages

- The apis will be used only in the framework layer
  of the Tizen Platform. Now they are used
  to handle power lock reference count. But
  it will be used for more information to handle
  resources of framework.

- The reference count is increased when power is locked
  and the reference count is decreases when power is ulocked.
  There are several reference counts for each service
  because power can be locked several times by the usage
  of other apis.

Change-Id: I38df55bcf0654647d7ecb34389a4db558dee6a9b
Signed-off-by: Taeyoung Kim <ty317.kim@samsung.com>