[API] Update C-API

[API] Update C-API

Update C-API and corresponding code changes

Major Changes:

1. ml_nnmodel_compile_with_conf() replaced with ml_nnmodel_construct_with_conf().
This new function loads the model from the config file but does not initialize.
ml_nnmodel_compile() should be called after ml_nnmodel_construct_with_conf() before training.

2. ml_nnmodel_compile() does not take optimizer as an input.
Rather, use ml_nnmodel_set_optimizer() to set the optimizer for the model.

3. init() from neuralnet has been updated to loadFromConfig() and does not initialize the model anymore.
Rather call init() after loadFromConfig() to initialize.
This also allows updating the model config after loading model with loadFromConfig().

4. init(optimizer, args_list) has been replaced with init()
Rather call setOptimizer(optimizer) to set the optimizer and
setProperty(args_list) to set the properties before calling init().

5. Bug fixes in checkValidation()

Signed-off-by: Parichay Kapoor <pk.kapoor@samsung.com>