Change default dev mode server to static implementation

[niloc132]

Starting in GWT 2.11 (see #9863 and #9866) a new dev mode server implementation was introduced - com.google.gwt.dev.shell.StaticResourceServer. At the same time, the JettyLauncher implementation was deprecated, and logs a warning to the console when used.

This ticket proposes that in GWT 2.13 the default be changed to StaticResourceServer, with the JettyLauncher left for at least one more version before being removed.

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As an alternative, we could remove the default server entirely and change to -noserver by default, so that any user specifying -server needs to also pick the server implementation they want to use.

[eliasbalasis]

I can see JettyLauncher etc. disappearing eventually, primarily in favor of external server wiring but also in relation to maintenance headaches and related struggles.