add option: declareModule, default true, to only get the moduleName

Usage: 
```js
.pipe(ngHtml2Js({
  moduleName: 'myApp',
  declareModule: false
}));
```

I am using the same module for my source file and my template files, and I don't want my compiled file to have 'try catch' everywhere.

This makes it so, if I set `options.declareModule` to false, it will generate templates which assume that the angular module named `options.moduleName` already exists.

Added a test for it as well. Let me know if you want anything changed, or don't like the API.