Prepare for CDL netlist export

Reviewed changes from #1049

SpiceLibCompDialog has been reworked to achieve the code quality
improvements introduced by #1049.

Tested the following dialogs under extsimkernel/:
-ExternSimDialog
-CustomSimDialog
-SimSettingsDialog
-SpiceLibCompDialog

-rebased

qucs/extsimkernels/customsimdialog.cpp

@@ -29,7 +29,7 @@
 /*!
  * \brief CustomSimDialog::CustomSimDialog class constructor
  * \param pc[in] Component that need to be edit.
- * \param sch[in] Schematic on which a_component presents.
+ * \param sch[in] Schematic on which component presents.
  */
 CustomSimDialog::CustomSimDialog(SpiceCustomSim *pc, Schematic *sch) :
     QDialog(sch),
@@ -119,7 +119,7 @@ void CustomSimDialog::slotChanged()
     a_isChanged = true;
 }
 /*!
- * \brief CustomSimDialog::slotApply Apply changes of a_component properties.
+ * \brief CustomSimDialog::slotApply Apply changes of component properties.
  */
 void CustomSimDialog::slotApply()
 {