common: Add ExpressionMatchTests unit tests

common: Add ExpressionMatchTests unit tests

Add ExpressionMatchTests class to test the functionality of
ExpressionMatch, helping ensure it works across Qt 4 and Qt 5.

This is implemented as a series of Q_ASSERT()'s as Quassel does not
yet have an actual testing framework.  Once a test framework is
settled on, this class can be migrated to unit tests.

To use ExpressionMatchTests:

1.  Include it in "quassel.cpp"

2.  Call ExpressionMatchTests::runTests() near end of Quassel::init()
// DEBUG: Run tests!
ExpressionMatchTests::runTests();