Add support for sbt-web 1.1.0
Upgrade to SBT native packager 0.7.4 so that we can remove workaround for old version of slf4j being pulled in. The workaround was itself causing problems by putting multiple versions of slf4j on the classpath
Tests overriding of FakeRequest Content-Type header

The Content-Type in the request was being overridden by a mixed order merge.
The actual problem was addressed in an earlier version of this commit, but
was addressed in #3119 before this commit passed legal review.

Fixes #3019.
Merge pull request #3207 from colindean/reverse-header-map-gh3019

Fixes overriding of FakeRequest Content-Type header
Improved translation tooling

* Can now specify the documentation translation version, this allows
  translating older versions of the documentation that don't include the
  tooling.
* Can now generate a translation report, which aids in translations.
Merge pull request #3225 from benmccann/packager074

Upgrade to SBT native packager 0.7.4
Update to sbt-web 1.1.0-RC1
Merge pull request #3223 from jroper/translation-updates

Improved translation tooling
Merge pull request #3228 from pvlugter/update-sbt-web

Update to sbt-web 1.1.0-RC1