Fix/delete branch #956

[shamikakumar]

In Branches page, added delete functionality for non-default branches. Fixes #956

[codecov-io]

Codecov Report

Merging #991 (cce67e3) into master (9623170) will decrease coverage by 0.33%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #991      +/-   ##
==========================================
- Coverage   44.56%   44.22%   -0.34%     
==========================================
  Files         142      140       -2     
  Lines       11547    11570      +23     
==========================================
- Hits         5146     5117      -29     
- Misses       5758     5804      +46     
- Partials      643      649       +6     

Impacted Files	Coverage Δ
config/logger.go	64.28% <0.00%> (-10.72%)	⬇️
catalog/mvcc/validate.go	88.23% <0.00%> (-6.21%)	⬇️
stats/collector.go	61.36% <0.00%> (-0.71%)	⬇️
api/handler.go	70.83% <0.00%> (ø)
gateway/operations/base.go	0.00% <0.00%> (ø)
catalog/mvcc/cataloger_merge.go	73.33% <0.00%> (ø)
catalog/mvcc/cataloger_delete_multipart_upload.go
catalog/mvcc/cataloger_get_multipart_upload.go
catalog/mvcc/cataloger_create_multipart_upload.go
gateway/multiparts/tracker.go	0.00% <0.00%> (ø)
... and 5 more

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[itaiad200]

LGTM
Great job @shamikakumar !