Update IrcCat's concurrency model

[initialcontext]

Updates IRCCat server with newer Java concurrency management mechanisms (ExecutorService) and process launch for Scripter (ProcessBuilder) to ensure less zombie thread buildup during long uptime.

Otherwise makes no changes to logic etc. Tested on my work IRC (where we use IRCCat a lot, thanks again!) and it seems to handle our current IRCCat bot's work quite nicely.