Allows the creation of multiple pipelines at once

This means the manager is only created once, so we'll connect much fewer times
when more than one document is uplodaded.

Fixes #48 and helps with #43 (there seems to be some other bottleneck for that
one; in my development environment it takes a long time to process lots of
files before they hit the send pipelines step, but maybe in the server this
will be less noticeable).
Removes worng return statement

We're not using the pipeline id for anything, and who would ever commit a for
loop with a return in it?
Return created pipeline id's
Merge pull request #53 from flavioamieiro/bugfix/improve-send-pipelines

Allows the creation of multiple pipelines at once