LogAnalyzer - add DataflashSQL

 - SQLAlchemy powered DataflashLog to sqlite database
   Full SQLAlchemy mapping.
   Importing data takes some time, but it improves data accessibility.
   Databases can be queried externally as well (sqliteman)
   or in ipython notebooks for development/debugging purposes.
 - ExampleAutotune as an example how to query/access data in a Test.

Many LogAnalyzer Tests could be reduced to a SQL query and the resulting message, if the database takes care of things.

I'm aware this adds SQLAlchemy as dependency,
I'm aware the time to import data to the database is a turnoff, 
but the ease of use is really convincing.