Renames StructuralVariantContext to SVContext.

[vruano]

This is more in-line with other SV class names.

Also SVContext.create is renamed to SVContext.of

[vruano]

@SHuang-Broad just a simple class rename and a method rename, so basically this just about whether you agree.

[codecov-io]

Codecov Report

Merging #3617 into master will increase coverage by 0.004%.
The diff coverage is 33.333%.

@@              Coverage Diff               @@
##              master    #3617       +/-   ##
==============================================
+ Coverage     79.766%   79.77%   +0.004%     
  Complexity     18233    18233               
==============================================
  Files           1224     1224               
  Lines          66966    66966               
  Branches       10449    10449               
==============================================
+ Hits           53416    53419        +3     
+ Misses          9327     9324        -3     
  Partials        4223     4223

Impacted Files	Coverage Δ	Complexity Δ
...ute/hellbender/tools/spark/sv/utils/SVContext.java	74.286% <33.333%> (ø)	19 <1> (?)
...e/hellbender/engine/spark/SparkContextFactory.java	71.233% <0%> (-2.74%)	11% <0%> (ø)
...oadinstitute/hellbender/utils/gcs/BucketUtils.java	79.87% <0%> (+3.247%)	39% <0%> (ø)	⬇️

[SHuang-Broad]

I like it. 👍