Add automated continuous integration testing using Travis CI

## Introduction
What is Travis and how to setup it (but I mostly done that part already):  
http://docs.travis-ci.com/user/getting-started/

It's completely free for open source projects:smiley: 
Example setup for my Lightning fork: https://travis-ci.org/kuc/Lightning-Browser/builds

## What this PR contains
* added missing `ant` project files
* fixed **errors** found by [android lint tool](http://tools.android.com/tips/lint).  
Warnings was around 100 so I haven't touched them (yet).
* configuration of Travis in `.travis.yml` file:  
currently Travis tests if project will be compiled successfully and android lint will not find any errors.

## How to enable Travis for `anthonycr/Lightning-Browser`
1) Sign up on https://travis-ci.org using your GitHub account
2) Enable testing this repo on https://travis-ci.org/profile/anthonycr
3) **Important**: Enable option "Build only if .travis.yml is present" on page https://travis-ci.org/anthonycr/Lightning-Browser/settings
4) Merge this PR. First build should start immediately :wink: