reports all sending error for mis-configurations

[flovilmart]

• Better report errors
• Make sure each sender reports properly their status (deviceType and deviceToken)

[codecov-io]

Current coverage is 87.78%

Merging #3 into master will decrease coverage by -0.23% as of 6821561

@@            master      #3   diff @@
======================================
  Files            5       5       
  Stmts          217     221     +4
  Branches        34      34       
  Methods          0       0       
======================================
+ Hit            191     194     +3
  Partial          1       1       
- Missed          25      26     +1

Review entire Coverage Diff as of 6821561

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