This commit provides APIs for user to use the widely used attribution methods to explain DL models and the evaluation methods to quantify the explanations. With combination of MindInsight, the user can have a friendly visualization on their models.

The SummaryRecord.add_value() method is extended to record the data of
MindExplain.

Signed-off-by: leonwanghui <leon.wanghui@huawei.com>