Add internal candidate helper APIs

Add internal candidate helper APIs

int watchface_editable_candidate_create(bundle **candidate, const char *name);
int watchface_editable_candidate_get_name(bundle* candidate, char** name);
int watchface_editable_candidate_set_color(bundle *candidate, watchface_editable_color_h color);
int watchface_editable_candidate_get_color(bundle *candidate, watchface_editable_color_h *color);
int watchface_editable_candidate_color_create(watchface_editable_color_h *color, int r, int g, int b, int a);
int watchface_editable_candidate_color_get(watchface_editable_color_h color, int *r, int *g, int *b, int *a);
int watchface_editable_candidate_color_destroy(watchface_editable_color_h color);
int watchface_editable_candidate_set_preview_image(bundle *candidate, const char *path);
int watchface_editable_candidate_get_preview_image(bundle *candidate, char **path);

Change-Id: If646190039135ac6b5962877ade974deb58e46c4
Signed-off-by: hyunho <hhstark.kang@samsung.com>