Added internal default charset definition to read XML in string
representation, because it must not be the same like
'DataStore.DEFAULT_CHARSET' which could be different in theory
Added test cases for method 'shutdown' which must not interrupt the
caller (should not throw an exception)
Added test cases for uncovered code

(belongs to issue #33)
Using utility 'Closeables' to close the given InputStream
Added test to cover the case that a browser regular expression is
without a subgroup definition and therefore the gathering of version
number is not possible

(belongs to issue #27)