[SE-100] change: small improvements to API

...e/java/ch/systemsx/cisd/common/array/MDAbstractArray.java

...on/source/java/ch/systemsx/cisd/common/array/MDArray.java

...ource/java/ch/systemsx/cisd/common/array/MDByteArray.java

...rce/java/ch/systemsx/cisd/common/array/MDDoubleArray.java

...urce/java/ch/systemsx/cisd/common/array/MDFloatArray.java

...source/java/ch/systemsx/cisd/common/array/MDIntArray.java

...ource/java/ch/systemsx/cisd/common/array/MDLongArray.java

...urce/java/ch/systemsx/cisd/common/array/MDShortArray.java

common/source/java/ch/systemsx/cisd/common/array/Test.java

...eTest/java/ch/systemsx/cisd/common/array/MDArraytest.java