Avoid SBT macro recompilation issue

[mlvn23]

If you add a method in the API, you'll get an error like this:

Request path: spatutorial/shared/Api/getTodos
Request path: spatutorial/shared/Api/getMessage
Request path: spatutorial/shared/Api/motd
Sending 4 Todo items
[error] p.c.s.n.PlayDefaultUpstreamHandler - Cannot invoke the action
scala.MatchError: Request(WrappedArray(spatutorial, shared, Api, getMessage),Map
(what -> java.nio.HeapByteBuffer[pos=0 lim=3 cap=3])) (of class autowire.Core$Re
quest)

SBT appears to have an issue in not incrementally compiling macros when its
dependents change. So in this case, the Router is dependent on Api trait,
and if that trait changes, all invocation to the Router needs to be recompiled.
The original Router invocation was in Application, but Application will probably
not change when you change the Api service. As a work-around, move it here because
if you change the Api trait, you will need to change the ApiService implementation,
so this entire file (including the router invocation) would have to be recompiled.

[mlvn23]

This would fix #23