Support for custom PB conditions

[CryZe]

With custom key value pair support, auto splitters can provide information such as deaths and score. By allowing to modify the PB condition the LiveSplit could be used in the following scenarios:

• Runs that minimize deaths
• Runs that maximize score
• Runs that minimize the amount of items (Low%)
• Runs that maximize time (originally requested here: Idea that could be added LiveSplitOne#695)

This is blocked for now on custom variables in general being support a bit better by livesplit-core (permanent storage in history, showing score on the timer instead of current time, ...)