Travis-CI integration.

Added integration with Travis-CI (free CI tool). Currently set up to run [JSHint](http://www.jshint.com/) for each push (and also on pull requests) using Grunt. See https://travis-ci.org/verath/NexBot for an example.

* To enable, Travis-CI must be activated for the repository. https://travis-ci.org/profile and flip the switch.
* Travis gives us a fancy build status icon. The current icon in the README.md file is pointing to verath/NexBot, and should be updated should this PR be merged.
* To run the tests locally one has to install Grunt by running `npm install -g grunt-cli` (a normal `npm install` is also required). After Grunt is installed, `npm test` will run all tests defined in the test task of the Gruntfile.js file (currently only jsHint).
* The jsHint settings are in the .jshintrc file in the root directory. The current file is more or less directly from the grunt-contrib-jshint repository, which one would assume is using good defaults.
* One can also override jsHint locally in a file, see http://www.jshint.com/docs/.
* Travis is configured using the .travis.yml file. Currently emails are disabled as they can be quite spammy.

This pull request also contains fixes for all the current jsHint violations. They were mostly small syntax "errors" or variables used out of scope.