Added Travis CI Support

## Examples

Correct Plugin Added: https://github.com/dufferzafar/picard-plugins-testing/pull/1

Incorrect Plugin Added: https://github.com/dufferzafar/picard-plugins-testing/pull/2

## Original Commit Message

Tests are run on all Travis supported versions of Python.

test.py contains 3 tests:

    generate_json:

        Generates the json data from all the plugins
        and asserts that all plugins are accounted for.

    generate_zips:

        Generates zip files for all folders and asserts
        that all folders are accounted for.

    valid_json:

        Asserts that the json data contains all the
        fields for all the plugins.
This file is automatically generated by `build_json`, isn't it? In that case I think it shouldn't be checked into the repository, and should be added to `.gitignore` instead.