Add global setting for max requests

[mattwiller]

Fixes #656

[boxcla]

Verified that @mattwiller has signed the CLA. Thanks for the pull request!

[coveralls]

Pull Request Test Coverage Report for Build 1763

• 6 of 6 (100.0%) changed or added relevant lines in 3 files are covered.
• 7 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.03%) to 58.793%

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Files with Coverage Reduction	New Missed Lines	%
src/main/java/com/box/sdk/BoxJSONResponse.java	2	93.33%
src/main/java/com/box/sdk/BoxAPIRequest.java	2	63.57%
src/main/java/com/box/sdk/RealtimeServerConnection.java	3	88.57%

Totals
Change from base Build 1759:	-0.03%
Covered Lines:	4607
Relevant Lines:	7836

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💛 - Coveralls