Maven project addition

I've added a Maven project so that:

1. Other IDEs can be used to develop jstock
2. One is able to easily compile and produce artefacts from the command-line.  
3. The use of Maven as a dependency management tool removes the need to store dependencies within the repository (ie. the `libs/` directory).  Storing in the `libs/` directory becomes an issue when multiple versions of those libs are used since each one becomes version controlled.  If this fork is pulled into JStock I recommend that all the dependencies should all be done in this Maven way.  

The dependencies such as blobsallad should also be setup as Maven projects so they can be:

1. Submitted to a global maven repository to be used as external dependencies.  That is, developers of JStock only see a maven coordinate for blobsallad (etc) and these get pulled down from somewhere like `https://repo.maven.com`.
2. To facilitate local development of blobsallad (etc), they can be installed to the local repository and the jstock under development will pull in this version.

This fork works in all aspects except for some peripheral ones as mentioned in the README.md (discussed as TODOs).  The README.md files contains usage instructions.

Please feel free to add any comments or requests for modifications here.  I feel this is a valuable addition to the fantastic jstock project and would like to see it adopted.