Fixed Exception dialog disapearing after a view second when exception occurs during app startup.
Problem was caused by splashscreen timeout, wx closing averything else if there is no more main frame.
Changes:
- no more timeout for splashscreen
- use wx.App OnInit method to give first operation to mainloop, object are then now created in mainloop
- main loop is then created _before_ showing splash screen
- no more wxyield or wx processevent tricks needed to display splash screen
- exception handler not blocking anymore on dialog (callafter)
- because of mainloop being there before everything, exit must be called explicitely if exception caught during startup -> exit parameter in handle_exception + try/except around startup calls

UNTESTED ON WINDOWS

                  <xsd:element name="Xenomai">
                    <xsd:complexType>
                      %(toolchain_gcc)s
                      <xsd:attribute name="XenoConfig" type="xsd:string" use="optional" default="xeno-config"/>
                    </xsd:complexType>
                  </xsd:element>