Enhance conjoin time joining options

[gsjaardema]

Modify conjoin such that user can specify how the times in the two or more databases will be combined:

• Current ending up with sequential monotonically increasing times.
• Take all from first databases and then monotonically increasing from later databases
• Interleave the times from all databases, output monotonically increasing
• Just concatenate times so not necessarily increasing, use all time s from all databases in order they appear...

If I have two exodus files with different time sequences i.e.

T = 1, 2, 3

And another

T = 1.5, 2.5 , 3.5

When I combine them will I get the sequence

T = 1, 1.5, 2, 2.5 …

Or will it just concatenate them?

1, 2, 3 , 1.5, 2.5 , 3.5

[gsjaardema]

Some work on this in #671 -- concatenate times. Can then sort them using io_shell or will add sort to conjoin later.