No longer strict compile demos (see below for details)

- We no longer inherit GWT's JUnit module which we should
have never done. In GWT 2.7, it will activate the remote
logger by default and it also causes other problems incl.
significantly increased code size:
https://developer.jboss.org/thread/235647

- We inherited it to make strict compiles pass since
errai-bus, errai-ioc etc. contain base classes that
aim to make testing Errai apps easier (i.e.
AbstractErraiTest). These base classes need the JUnit
module and won't strict compile without it. However,
this is not a problem for testing as the JUnit module
is inherited automatically when running GWTTestCase.

- For now, apps that need strict compilation need to
inherit the JUnit module until we provide a seperate
test module and move our test base classes into this
new module.