"Generate sequence" utility is too slow

I tried to generate large test sequences using Tools->Generate sequence menu to test memory overflow issues and found that it works incredibly slow and has 0 tests.

The reasons why it works slow:

1) Fasta file writer is very slow because it reads every FASTA line from the DBI.
2) Random sequence generator algorithm is too slow: takes 6 seconds to generate 100mb on my computer in debug mode which is unacceptable for a such simple task.

The task is to optimize these trivial places and add performance counters into the code.