New beforeUpload event - makes it possible to validate files before the upload starts

[eivindr]

Can be used for validating files sizes - see basic example. Can also be used for more advanced size checking (by file extension).

Calling uploadingFile.setAbort() from the event will abort the upload (xhr.send is not called) and the file is removed from the queue.

[jkuri]

@eivindr thanks alot! can you bump version in package.json also please? then I'll merge and publish to npm.

[jkuri]

Thanks, published 1.5.4 to npm.

[inigopascall]

Trying to use this function as per the example I am getting Type 'EventEmitter<{}>' is not assignable to type EventEmitter<uploadedFile>" Type '{}' is not assignable to type 'UploadedFile' Property 'id' is missing in type '{}' during the build process

[inigopascall]

Going into node_modules/ng2-uploader/src/services/ng2-uploader.ts and changing line 87 from _beforeEmitter: EventEmitter<UploadedFile> = new EventEmitter();

to

_beforeEmitter: EventEmitter<any> = new EventEmitter();

Fixes the problem for now.

[jkuri]

thanks, 0d4433a and published.