XDebuggerSettingsManager — don't save defaults

XmlSerializerImpl — introduce serializeIfNotDefault — new method allows us to return null if element is empty (we don't need to create empty element and then check it)
reliably call exit()
testdata for IDEA-65386
final field initialization: class initializers (IDEA-130312)
initialized twice should not make use of computed constants (IDEA-63226)
better painting for bread crumbs
bytecode-viewer: consistent wording, better description