initial add of .travis.yml

So I don't think that this is in a position to be pulled, but I am looking for some feedback. There was a request for travis-cl integration, and seeing that we should at least make sure the project compiles whenever new code is added (for instance, I accidently broke the project last night with my previous commit - it is fixed in this version btw), I thought I would make travis work.

So on the upside travis works, I added a `.travis.yml` and set up an android environment so everything can build. I have added an `android.jar`, which I think is awful, because I don't know of a way to find the ANDROID_HOME variable. Does anyone have an idea of how to do this on travis-cl?

Also, I added a whole new task to the `build.xml`, which i didn't really want to do. Is the `build.properties` file auto-generated? I only ask because the android sdk is in the downloads folder.. 

I want to make this integration work well, but it is my first time working with travis, I hope everyone can take a look at this!