B2g-util

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**Features and Improvements**

- Add b2g_flash_taskcluster

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**Features and Improvements**

- Add space in filepath support for AdbWrapper's pull and push.
- Add pending/submitted filepath into result dict object for get_crashreports.

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**Features and Improvements**

- Add keep profile feature of b2g_shallow_flash.
- Remove gecko.mstone value from pref.js when backup profile.

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**Features and Improvements**

- Add b2g_shallow_flash tool.
- Add adb remount and adb wait-for-device.
- Modify the decompressor's method to classmethod.

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- missing some files...

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**Features and Improvements**

- Modify tools for more reusable.
- Refactoring.
- Add JSON output for get_crashreports.

**bugfixes**

- Remove unused import.
- Fix the docstrings from single-quoted to double-quoted string format.