Closes #236 by setting a default SQLAlchemy URL

tracim/development.ini.base

 # sqlalchemy.url=mysql://username:password@hostname:port/databasename
 # sqlalchemy.url = postgresql://tracimuser:tracimpassword@127.0.0.1:5432/tracimdb?client_encoding=utf8
 # sqlalchemy.url = mysql+pymysql://tracimuser:tracimpassword@127.0.0.1/tracimdb
-sqlalchemy.url = <replace_database_uri_here>
+sqlalchemy.url = sqlite:///tracimdb.sqlite
 
 #echo shouldn't be used together with the logging module.
 sqlalchemy.echo = false