RAMPART fails if kmer value is too large for assembler

[maplesond]

If the user specifies a kmer size that is too large to deal with RAMPART will fail when that assembly is executed. We should think of a more graceful way of handling this problem.

One idea would be to "fail early" by checking that the assembler can handle the kmer value before anything in RAMPART is executed. Another option would be to ignore the failed assembly and continue on regardless.