Add battery information accessors #83

This is a

• Bug report
• Question
• Feature Request

Summary

• Add battery information accessors java-client#882

Environment

• ruby_lib_core version:
• Mobile platform/version/device under test:

Actual behaviour and steps to reproduce

Expected behaviour

Link to Appium/Ruby logs

Create a GIST which is a paste of your full Appium logs, and link them here.

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