Updating SeqSiftTestCase.

Updating the assertSameData method of SeqSiftTestCase to accept
sequence generator functions.
Adding sequence modificatino functions.

Adding seqsift.seqops.seqmod which has two functions: seq_mod and
remove_gaps. seq_mod allows character translations and deletions
to sequence strings. remove_gaps uses seq_mod to strip all gaps
from sequences.
Updating SeqSiftTestCase.

Updating assertSameData method of SeqSiftTestCase to not compare
sequence descriptions by default.