Add a config option to retain the entire IntelliJ instance untouched at the end

[PawelLipski]

There's only probe.paths.logExport, somewhat related... but apparently nothing to avoid the removal completely.

Esp. important in local runs — to inspect the local contents easily, and to avoid errors like:

UITestSuite STANDARD_ERROR
   ...
    java.io.IOException: [1] Failure while deleting /var/folders/wm/_61wp3jn3s7f8jh9x119ssp40000gn/T/ide-probe/instances/intellij-instance-241.13688.18--LYi5Na5HTVe67o3dg-QswA at dir  /var/folders/wm/_61wp3jn3s7f8jh9x119ssp40000gn/T/ide-probe/instances/intellij-instance-241.13688.18--LYi5Na5HTVe67o3dg-QswA/Contents
        at org.virtuslab.ideprobe.ProbeExtensions$DeletingVisitor.$anonfun$postVisitDirectory$2(ProbeExtensions.scala:273)
        at org.virtuslab.ideprobe.ProbeExtensions$DeletingVisitor.$anonfun$postVisitDirectory$2$adapted(ProbeExtensions.scala:271)
        at scala.util.Success.foreach(Try.scala:260)
        at org.virtuslab.ideprobe.ProbeExtensions$DeletingVisitor.postVisitDirectory(ProbeExtensions.scala:271)
        at org.virtuslab.ideprobe.ProbeExtensions$DeletingVisitor.postVisitDirectory(ProbeExtensions.scala:249)
        at java.base/java.nio.file.Files.walkFileTree(Files.java:2828)
        at java.base/java.nio.file.Files.walkFileTree(Files.java:2882)
        at org.virtuslab.ideprobe.ProbeExtensions$PathExtension.delete(ProbeExtensions.scala:170)
        at org.virtuslab.ideprobe.ide.intellij.DownloadedIntelliJ.cleanup(InstalledIntelliJ.scala:232)
        at org.virtuslab.ideprobe.IntelliJFixture.$anonfun$cleanupIntelliJ$1(IntelliJFixture.scala:92)
        at org.virtuslab.ideprobe.IntelliJFixture.withRetries(IntelliJFixture.scala:111)
        at org.virtuslab.ideprobe.IntelliJFixture.cleanupIntelliJ(IntelliJFixture.scala:92)
        at org.virtuslab.ideprobe.RunningIntelliJPerSuiteBase.$anonfun$teardown$3(ClassFixtures.scala:45)
        at org.virtuslab.ideprobe.RunningIntelliJPerSuiteBase.$anonfun$teardown$3$adapted(ClassFixtures.scala:45)
        at scala.Option.foreach(Option.scala:437)
        at org.virtuslab.ideprobe.RunningIntelliJPerSuiteBase.teardown(ClassFixtures.scala:45)
        at org.virtuslab.ideprobe.RunningIntelliJPerSuiteBase.teardown$(ClassFixtures.scala:39)
        at com.virtuslab.gitmachete.uitest.UITestSuite$.com$virtuslab$gitmachete$uitest$UISuite$$super$teardown(UITestSuite.scala:34)
        at com.virtuslab.gitmachete.uitest.UISuite.teardown(UISuite.scala:21)
        at com.virtuslab.gitmachete.uitest.UISuite.teardown$(UISuite.scala:21)
        at com.virtuslab.gitmachete.uitest.UITestSuite$.teardown(UITestSuite.scala:34)
        at com.virtuslab.gitmachete.uitest.UITestSuite.teardown(UITestSuite.scala)
       ....