Add travis CI integration and badge on readme to auto run tests

[nathan-hekman]

From Robert:
https://github.com/watson-developer-cloud/ios-sdk/blob/master/.travis.yml
https://docs.travis-ci.com/user/encrypting-files/

notice this command: - openssl aes-256-cbc -K $encrypted_1ae11c268751_key -iv $encrypted_1ae11c268751_iv -in WatsonDeveloperCloudTests/Credentials_full.plist.enc -out WatsonDeveloperCloudTests/Credentials.plist -d actually deencypts the file

make sure you git ignore Credentials.plist so you don’t automatically check it into the project

you will probably want every developer to have Credentials.plist file on their filesystems, however. The Xcode project will contain a reference to it