Turn on warning unused imports and remove unused imports

[codecov-io]

Codecov Report

Merging #149 into master will not change coverage. The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #149   +/-   ##
=====================================
  Coverage       0%     0%           
=====================================
  Files          27     27           
  Lines        1906   1906           
  Branches        5      5           
=====================================
  Misses       1906   1906

Impacted Files	Coverage Δ
...c/main/scala/vegas/render/StaticHTMLRenderer.scala	0% <ø> (ø)	:arrow_up:
...e/src/main/scala/vegas/render/WindowRenderer.scala	0% <ø> (ø)	:arrow_up:
core/src/main/scala/vegas/DSL/ConfigDSL.scala	0% <ø> (ø)	:arrow_up:
flink/src/main/scala/vegas/flink/Flink.scala	0% <ø> (ø)	:arrow_up:
...src/main/scala/vegas/render/BaseHTMLRenderer.scala	0% <ø> (ø)	:arrow_up:
core/src/main/scala/vegas/spec/package.scala	0% <ø> (ø)	:arrow_up:
core/src/main/scala/vegas/DSL/package.scala	0% <ø> (ø)	:arrow_up:
...src/main/scala/vegas/macros/ShowRenderMacros.scala	0% <ø> (ø)	:arrow_up:
core/src/main/scala/vegas/package.scala	0% <ø> (ø)	:arrow_up:

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[oshikiri]

@aishfenton @dbtsai @rgbkrk Could you please review this?

[rgbkrk]

Looks like a great cleanup. I'll trust in you and CI for the validity of removals. 😄

[oshikiri]

@rgbkrk Thanks!!