[CAPI] Propose save/load api

[CAPI] Propose save/load api

**Motivations**
1. Fine grained api required to save and load

**Changes proposed in this PR:**
- Add function to model.h  / `save`, `load`
- Mark `readModel()` deprecated (later remove...)
- Mark `saveModel()` to change `exportTo`
- Add `ModelSaveLoadFormat`
- Create capi-machine-learning-training-tizen-internal for internal api
support

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

Signed-off-by: Jihoon Lee <jhoon.it.lee@samsung.com>