Performances issues with large projects improved

Details: <p><strong>Testing:</strong></p><p>Using a large project (Some of Wendel&#39;s large projects are&nbsp;a good examples....) do teh following and check if responsiveness is acceptable.</p><p style="margin-left: 40px;">- Project should open faster once progress wheel has disappeared</p><p style="margin-left: 40px;">- Display parts-list</p><p style="margin-left: 40px;">- From parts-list, change TAG value (You may need to un-hide &#39;Tag&#39; column to do that...)</p><p style="margin-left: 40px;">- Run renumbering.</p><p style="margin-left: 40px;">- Display terminal strip (even better if there is a stacked one...) and proceed to do operations in it (move terminals, insert some, delete some, etc.)</p><p>Results of this test is subjective: lag should be &#39;acceptable&#39;.&nbsp; (Changing a tag from Windel&#39;s project&#39;s parts-list used to make SkyCAD hang for 30 sec and more... That is not acceptable...)</p>