Extracted trabian-webapp-core to new repo

https://github.com/trabian/trabian-webapp-core
Use git submodules for trabian-webapp-core

To pull the submodule run the following:

`git submodule update --init`

(Subsequent uses don't require the --init flag.)
Updated trabian-webapp-core submodule

The change to the submodule was minor (added a .travis.yml file) but
this is a demonstration of pulling the latest version from within the
submodule directory and then updating the submodule.
Merge branch 'extract_core'