Rewrite backend.

This commit improves the code structure and documentation of essential modules
/ classes.

* All methods needed to setup a BLAST env and run BLAST is available in SequenceServer module.
  * Remove DatabaseFormatter.
  * Blast is now mixed into SequenceServer instead of SequenceServer::App.
* SequenceServer::App forms the HTTP entrypoint to SequenceServer.
* bin/sequenceserver, now using Slop, provides an extensive CLI.
  * Can list databases we have and un-formatted FASTA and format them.
  * TODO: sequencerver init
  * Possible to use both config file and CLI switches. Options will be merged. CLI takes preecedence.
* Symbolize keys from config.yml. Makes for easy merging of

Cosmetics:
* Add SequenceServer#verbose?
* Define SequenceServer::Logger as a subclass of Logger - preserving our
  formatting style.

SS interactive. More CLI options.

write config file

Signed-off-by: Anurag Priyam <anurag08priyam@gmail.com>