Feature search component

I feel that get every module by mouse is too inconvenient, so I add a search linedit above the component listview. It matches all the module name contains the search text.
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This is another issue, during the modification, I found that there are some redundant code inside qucs.cpp, escpecially about "paintings", which seems obviously redundant codes. The comment around it is not consistent with the source. I just modify some of them and I think a closely review is required.