DragnDrop Upload text style

The 8px margin was uggly.

Replaces https://github.com/owncloud/core/pull/10037 also includes the change pointed out by @MorrisJobke in https://github.com/owncloud/core/pull/10037#issuecomment-50606480

@nstamm @MorrisJobke @jancborchardt @PVince81