WORK_DIR and BUILD_DIR now externalised

No longer hard coded for Travis / my local, these envvars now get
passed in, although BUILD_DIR defaults to the current directory.
Modify Travis config to use external envvars

Need to actually test that this approach works by actually
doing it!
Make sure script doesn't fail for now with no WORK_DIR
Fail the build if CI deps don't install
Fix some script issues
Simplify the way dirs are passed through env
Fix typo in travis config
Fix build.xml to add env to other shell tasks
Remove work dir again
Rename Railo start task for consistency
Wait for Railo to stop for shared environments
Allow Railo/MXUnit URLs to be passed in

In addition support local file URLs to these resources, for example
to save downloading every time when using local Jenkins install.
Pass URLs through build.xml
Merge pull request #4 from marcins/feature/generic-ci-helper

Make the CI Helper script more generic