implement search options button (issue #204)

* generalized specifying icon name in ConfigureOptionsAction constructor
* added IconButton "ActionIcon" constructor overload for creating opaque buttons
* made OptionsConstructor::SEARCH_KEY public
* fixed typo in doc comment for OptionsConstructor::DIALOG constant
* added SEARCH_OPTIONS key to icon_mappings.properties
    * resources/org/limewire/gui/resources/icon_mapping.properties

NOTE: regarding ConfigureOptionsAction class
  the icon name "LIBRARY_SHARING_OPTIONS" hard coded into the ConfigureOptionsAction
      constructor was factored out to make this constructor more general
  it was called in only three places so this accounts for the modifications to:
    * src/com/frostwire/gui/library/AbstractLibraryTableMediator.java
    * src/com/frostwire/gui/library/LibraryExplorer.java
    * src/com/frostwire/gui/library/LibraryPlaylists.java

again many whitespace only changes
to be clear tho the only visibility change i made was to that one additional OptionsConstructor::SEARCH_KEY - both of the ConfigureOptionsAction classes constructors (PR #361) were already public and the some of the OptionsConstructor constants LIBRARY_KEY, SHARED_KEY, and CONTENT_FILTER_KEY were already public and used outside the class in:
  LIBRARY_KEY =>
    * src/com/frostwire/gui/library/AbstractLibraryTableMediator.java
    * src/com/frostwire/gui/library/LibraryFilesTransferHandler.java
    * src/com/frostwire/gui/library/LibraryPlaylists.java
    * src/com/limegroup/gnutella/gui/options/panes/TorrentSaveFolderPaneItem.java
  SHARED_KEY =>
    * src/com/frostwire/gui/library/LibraryExplorer.java
  CONTENT_FILTER_KEY =>
    * none