Exclude specific packages and crossbuilds

 - see http://stackoverflow.com/questions/20189211
 - list of dependencies excluded found here:
  http://bit.ly/1lEd6e7

Also, the test project now doesn't complain about crossbuilds anymore. This is what I got before:

    sbt update
    // ... <snip> ...
    [error] Modules were resolved with conflicting cross-version suffixes in {file:/tmp/dwizard/dropwizard-scala-test/}dropwizard-scala-test:
    [error]    com.wordnik:swagger-annotations _2.10.0, _2.9.1
    [error]    com.wordnik:swagger-jaxrs _2.10.0, _2.9.1
    [error]    com.wordnik:swagger-core _2.10.0, _2.9.1
    [error]    com.fasterxml.jackson.module:jackson-module-scala _2.10, <none>
    [trace] Stack trace suppressed: run last *:update for the full output.
    [error] (*:update) Conflicting cross-version suffixes in: com.wordnik:swagger-annotations, com.wordnik:swagger-jaxrs, com.wordnik:swagger-core, com.fasterxml.jackson.module:jackson-module-scala
    [error] Total time: 15 s, completed 20-May-2014 16:28:48

Also, previously the workaround in the test project was to exclude the offending packages, but this wasn't a sustainable solution.

    "uk.gov.gds" %% "dropwizard-scala" % "1.0.0-SNAPSHOT" exclude("com.wordnik", "swagger-core_2.9.1") exclude("com.wordnik", "swagger-jaxrs_2.9.1") exclude("com.wordnik", "swagger-annotations_2.9.1")