Make SlideList extend interface Serializable

I'll be transmitting these over an OIS/OOS setup, so serializability is
crucial.

I'll be auditing DERSL and BSS to ensure that all fields are either
serializable or computable from serializable fields.
Make ColorScheme serializable

Used in DERSL
Make Event serializable

Map fields are changed to HashMap (HashMap is serializable; Map is not
by default).
Make EventResults serializable

As in Event, Map fields are changed to HashMap. Variables that are
directly assigned to the Map fields are also changed to have type
HashMap (they're method local variable that get HashMaps assigned to
them anyways).
Make BuildableStackedSlide.Chunk extend interface Serializable