Taskcluster-util

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**Features and Improvements**

- Check the credentials does or doesn't expired, and print on console.

**Bugfixes**

- Raise exception when loading credentials file error.

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**Bugfixes**

- Clean the cache of dest_dir and download_file_list after downloading.

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**Features and Improvements**

- Provide a way to give TaskCluster builds to Bitbar (Bug 1189354).

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**Features and Improvements**

- Modify the class for inheritance.

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**Features and Improvements**

- Modify the logger and gui of taskcluster_traverse.

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**Features and Improvements**

- Move tc_credentials.json to User's Home folder.
- Update README file.
- Update usage.
- Modify the Credentials input GUI of taskcluster_traverse.