feat(BUX-51): minercraft_api and minercraft_custom_apis in config

[witalij-4chain]

minercraft_api and minercraft_custom_apis for bux-server configuration.
mApi or Arc(case insensitive) can be used for minercraft_api


Miner's configuration can be overwritten by minercraft_custom_apis

[codecov]

Codecov Report

Merging #272 (b7e8634) into master (773234c) will increase coverage by 0.00%.
The diff coverage is 33.33%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #272   +/-   ##
=======================================
  Coverage   32.48%   32.48%           
=======================================
  Files          41       41           
  Lines        1373     1382    +9     
=======================================
+ Hits          446      449    +3     
- Misses        905      909    +4     
- Partials       22       24    +2     

Flag	Coverage Δ
unittests	32.48% <33.33%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
config/config.go	100.00% <ø> (ø)
config/services.go	33.83% <33.33%> (-0.02%)	⬇️

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[mrz1836]

LGTM