Cleaned up all the warn-unused and warn-unused-import issues

[norbert-radyk]

The change is a pure cleanup change (no functional changes) to fix the problems reported by the unused checks (-Ywarn-unused and -Ywarn-unused-import) and enforcing the checks by adding -Xfatal-warnings (will result in a compilation error should any new unused code section be introduced).

In some cases (where the method is a public one and can be overriden by the client) in order not to break the API removing the warning required marking the parameter explicitly as unused based on a solution proposed here: https://stackoverflow.com/questions/46128561/excluding-type-evidence-parameters-from-analysis-in-scala-when-using-ywarn-unus

[xuwei-k]

Maybe missing s interpolation 🤔 ?

squeryl/src/main/scala/org/squeryl/logging/BarChartRenderer.scala

Lines 111 to 113 in 7b2b170

	function drawVisualization() {{
	{Unparsed(funcCalls(stats))}
	}}

          function drawVisualization() {{
-            {Unparsed(funcCalls(stats))}
+            ${Unparsed(funcCalls(stats))}
          }}

[xuwei-k]

I think "-Xfatal-warnings" and IdOps are too much 😕

[norbert-radyk]

Hi @xuwei-k, I have addressed all the changes you requested by removing -Xfatal-warnings and IdOps and cleaning up the BartChartRenderer to use correct string interpolation.

I believe there would be a some value in having the fatal warnings being switched on, but you're probably right that the obfuscation it leads to (by the means of adding IdOps) is too much. So let's just treat this merge request as a cleanup of the unused code.

[xuwei-k]

Hmmm 🤔 I think some (not private method) parameters (e.g. ev: CanCompare[T1, T2] ) has meaning. Don't remove these params.
Could you please separate more small pull requests? (e.g. "remove unused imports", "add return type annotations", "remove unnecessary comments")

[norbert-radyk]

Thanks @xuwei-k for the feedback. Having separate merge requests for the smaller sets of changes is a fair point. I am going to close this one and have raised a small one for the fix on the BarChartRenderer which was failing with the unused import: #248