Add records to record arrays in a runloop

When adding records just after loading them, the elements in the UI
might have to be updated, which may trigger `get` on associations right
away. As an effect, even if we load a few records on an event (like
repository on build:started event), ember model may end up fetching the
record.

This commit fixes such occurrences by adding record to record arrays in
a run loop, so newly created records will be added at once, after the
event was served.