Did the Democratic party devise the 'super-delegate' system to ensure they...

[Heidi 4]

...maintain control? and always be in a position to elect those they believe will adhere to the 'party line'? (as opposed to what the people want)

It appears to me this is the most discongomerated system ever devised to make a mockery of the popular vote and hold the reins on anyone who will oppose the party chairmen from ever oppose them on any & every issue.

[todp03]

of course, now no matter who wins the popular vote,they can still pick the nominee

[Steve S]

Initially the super delegate system was the only system in place for choosing the next presidential candidate. In 1968, after the party chose a couple candidates that were not well received by the public, the party devised the idea of allowing people to choose their candidate in elections, but maintained some semblance of control through superdelegates. Only in a close election can the superdelegates choose the candidate who better "toes the party line". This way they can still have their say, but the candidate will always be electable.

So, your hypothesis is somewhat backwards, the superdelegate system wasn't created so they would maintain control of who got nominated, the delegate system was created to limit their control.