clean up java warnings

a number of bits of java code:
```
:base:compileTestJava/home/beakerx/kernel/base/src/test/java/com/twosigma/beakerx/chart/categoryplot/plotitem/CategoryAreasTest.java:63: warning: non-varargs call of varargs method with inexact argument type for last parameter;
categoryArea.setBase(Arrays.asList(array1));
^
cast to Object for a varargs call
cast to Object[] for a non-varargs call and to suppress this warning
/home/beakerx/kernel/base/src/test/java/com/twosigma/beakerx/chart/categoryplot/plotitem/CategoryBarsTest.java:64: warning: non-varargs call of varargs method with inexact argument type for last parameter;
categoryBars.setBase(Arrays.asList(array1));
^
cast to Object for a varargs call
cast to Object[] for a non-varargs call and to suppress this warning
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
2 warnings
```