Adds custom broker setting

[Koed00]

• You can now configure a custom broker class using the broker configuration setting.
• Also fixes a Rollbar configuration problem

[codecov-io]

Current coverage is 96.35%

Merging #141 into master will decrease coverage by -0.24% as of 3ca5a23

@@            master    #141   diff @@
======================================
  Files           39      39       
  Stmts         2703    2718    +15
  Branches         0       0       
  Methods          0       0       
======================================
+ Hit           2611    2619     +8
  Partial          0       0       
- Missed          92      99     +7

Review entire Coverage Diff as of 3ca5a23

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