Branches support for BitBucket

[qwerty287]

Resolve two TODOs by loading branches from BitBucket servers.

[codecov-commenter]

Codecov Report

Merging #907 (5d04eca) into master (6568751) will decrease coverage by 0.14%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #907      +/-   ##
==========================================
- Coverage   51.85%   51.70%   -0.15%     
==========================================
  Files          80       80              
  Lines        6073     6090      +17     
==========================================
  Hits         3149     3149              
- Misses       2743     2759      +16     
- Partials      181      182       +1     

Impacted Files	Coverage Δ
server/remote/bitbucket/bitbucket.go	90.14% <0.00%> (-4.45%)	⬇️
server/remote/bitbucketserver/bitbucketserver.go	0.00% <0.00%> (ø)

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