SequenceServer MAKEBLASTDB wrapper was working in two-steps:
1) invoke #scan - this was eagerly scanning for formatted,
  unformatted and DBs that may require reformatting and storing
  them in instance variables
2) whenever any makeblast operation was performed, it relied on scan
  being run beforehand to populate the instance variables and was
  using these values to perform listing, formatting and reformatting
  operations.

When SequienceServer.init was invoked (any time the web server starts
or the CLI binary is launched) it was calling makeblastdb.scan regardless
of whether it will format/reformat the databases. This was rather slow
on large database dirs (I saw upwards of a minute on a large dir).

This change refactors MAKEBLASTDB wrapper to only scan for DBs to format
or reformat when it is actually going to perform any of these operations.

Now the class does not rely on running #scan beforehand to perform any
operations, and invokes the data gathering methods lazilly (i.e. only
when gathering data is required), making sure it does not perform
any slow operations when they are not necessary.