Tests: Simplify the cmake file

Now that the dependeny to the main window is removed from the
DBBrowserDB class we can get rid of all the dialogs and widget related
stuff in the cmake file used for the unit test project. Because our
Application class depends on the main window, too, the code for the CSV
tests is changed to use Qt's standard QApplication class.

src/tests/TestImport.cpp

@@ -1,7 +1,7 @@
 #include <QTemporaryFile>
 #include <QtTest/QTest>
+#include <QApplication>
 
-#include "Application.h"
 #include "TestImport.h"
 #include "../sqlitedb.h"
 
@@ -17,7 +17,7 @@ void TestImport::csvImport()
     // Init basic application
     int argcount = 1;
     const char* appname = "sqlb-unittests";
-    Application app(argcount, const_cast<char**>(&appname));
+    QApplication app(argcount, const_cast<char**>(&appname));
 
     // Create temporary CSV file
     QTemporaryFile file;