Simplify of the SimpleMsgTest.

* Make use @Before to prepare PrintStream and OutputStream for each test.
* Shortening the names used in the tests
Detailed assertion in SimpleMsgTest

Signed-off-by: Grzegorz Wieczorek <grw1@wp.pl>
SimpleMsg improvements

* Improve printing when msgContend is Collection<Loggeable> or Loggeable[]
* Allowing the use of nullable msgName in order to produce output like:
   <tag>Some Value</tag>
* Add a constructor just with tagName and msgContent
Handling when msgContent is null instead of throwing NPE

* if msgContent is null then <tag name="Some Name"/> is printed
* if entry of composite msgContent is null then:
    <tag name="Some Name">
      <inner-tag name="Inner Name">
        Some Value
      </inner-tag>
      null  <- it's that null entry
    </tag>
Simplify of SimpleMsg

Removing unnecessary costructors
Adding additional tests to SimpleMsgTest