Some build fixes and cleanup.

AdRulesIMASampleApp/src/main/java/com/brightcove/player/samples/ima/adrules/MainActivity.java

  * Corrected some comments.

BasicFreeWheelSampleApp/src/main/java/com/brightcove/player/samples/freewheel/basic/MainActivity.java

  * Unused import.

BasicIMAWidevineSampleApp/src/main/AndroidManifest.xml
BasicWidevineSampleApp/src/main/AndroidManifest.xml

  * Corrected minSdkVersion.

build.gradle

  * Updated dependencies to work with 4.0.15 artifacts.

gradle.properties

  * Turned off runHLSPlayerSampleApp until artifacts are corrected.

settings.gradle

  * Wrapped flags with Boolean conversion.