Updated Search Bar Style

Please note that I don't feel that the search bar needs to be skinned by
users, hence why it is not part of the large css-skinning project. I
also feel that given the PR #416 a new search bar with highlight the new
search functionality.

Updated the look of the search  bar:
+ larger, curved edges
+ changes color when has focus
+ search icon built into search
- removed "Search For" text in lieu of search icon

cockatrice/src/tab_deck_editor.h

@@ -85,7 +85,6 @@ private:
     QTreeView *deckView;
     KeySignals deckViewKeySignals;
     CardFrame *cardInfo;
-    QLabel *searchLabel;
     SearchLineEdit *searchEdit;
     KeySignals searchKeySignals;