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