Added bower.json file to register the package

Hi, 

I've added a bower file to publish your TableDnD package in bower's repository.

After merging this pull request you can easily publish the package to bower by running these commands:

```bash
sudo npm install -g bower # only if you have not installed bower
bower register TableDnD https://github.com/isocra/TableDnD
```
or just merge this pull request and then I can publish the package for you as bower does not need authentication

thanks!