Archive only compressed files. Fix #2

The tool stored mbox files twice: compressed and uncompressed.
With this commit, downloaded contents are only stored compressed
(even when they are uncompressed on the origin).

MBoxArchive instance provides a new property container() which
returns a container to the compressed archive. This container
is a file descriptor that will decompress the content on the fly.
This means that MailArchiveAnalyzer does not recive a filepath to the
mbox anymore. It gets a a MBoxArchive object to parse the content from
it.

Unit tests were also updated.
Fix error retrieving local mboxes
Store real path instead of the relative path for local mboxes
Merge pull request #34 from sduenas/compressed-mboxes

Archive only compressed files. Fix #2
Use get_database instead of create database
dbn: Add new database module/definition using SqlAlchemy
dbn: Add session implementation to integrate the new database
dbn: Add class Report for generating reports from the database
Integration of SqlAlchemy classes in mlstats
ci: Update .travis.yml for continuous integration
dbn: Remove unused methods
Remove old database code
db: Move new database implementation in the old namespace

Last step to replace the old database implementation with
SqlAlchemy
db: Force convert to unicode for MySQL dialect
Simplify logging information
Remove admin parameters to the create database

Since SqlAlchemy, we will rely on the user to create the
database, though we will create the tables if they don't
exists. Therefore, this option does not makes sense anymore.
tests: Update tests according to latest changes in analyzer

We now returns a datetime instead of a ISO string, therefore,
the test should reflect that comparison
setup: Update meta data