Added gulp for building tasks - Fix #41

I've added support for gulp.

The current tasks are the same as the makefile, but it also minifies html, css and concatenates js files. It also uses the plugin for angular-templatecache.

I had to modify the references to files where you use the question mark. I think this is not going to be needed anymore since I had added the gulp-rev plugin which is used with usemin.

Considerations:

1 - You'll need to run "gulp templates" at least once in order to run the server since the app won't find the templates. Probably we can commit the js/partials.js file generated by this task.

2 - Js uglification was not possible. I think this can be solved by linting the js files. This wouldn't be a hard task, but a tedious one :).

3 - I've tried to emulate the tasks you have on the makefile. The "bump" task will replace the version numbers according to the one on package.json. Please tell me what you think about it.

I'll expect your comments on this.

cheers.