[ ActFunc ] Separate Activation Function from Activation Layer

[ ActFunc ] Separate Activation Function from Activation Layer

In order to use Activation function method in other Layer, it is
better to make sepearte the activation function definition and Layer.
In this PR, new ActiFunc Class is introduced and midified the
activation layer to use it.
RNN Layer also use this as an private variable.

**Self evaluation:**
1. Build test:	 [X]Passed [ ]Failed [ ]Skipped
2. Run test:	 [X]Passed [ ]Failed [ ]Skipped

Signed-off-by: jijoong.moon <jijoong.moon@samsung.com>