make LS2 to keep its own copy of LSMethod

:Release Notes:
LS2 now keeps own copy of passed LSMethod. Thus easing life for
dynamically registered methods.

:Detailed Notes:
- introduced LSMethodEntry for storing callback info
- copy method name for callback

:Testing Performed:
unit-tests on desktop

:QA Notes:

:Issues Addressed:
[BHV-4021] Re-factor LS2 to keep its own copy of LSMethod info

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <nikolay.orliuk@lge.com>

Change-Id: I66381c83e754f63df707342e5ee4934bdf8c17da
Reviewed-on: https://g2g.palm.com/5228
Reviewed-by: DCO Verification
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Tested-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>