Some major changes in the database structure

* Removed venue from the database (non-important for the first sight)
* event_date column renamed to event_start_date
* Added event_end_date column (for past event filtering functionality, will be implement in the nearest future)
* Added convert_date_api_to_sqlite function
* For start and end date now there is only date, no time (only date is important for the first sight)
* Making report for the first run, just list of all the events
Working on limits

* Added warning if artists limit is too small
* Added limit option for artist.getevents API method and set it to 1000, must be enough for any artist
Now past events are not getting to the report page
Added lastfm_api_call function to simplify API calls
Fixed indentation, modified .gitignore, refactoring
Removed end_date, stick to a different solution for past events filtering
Finally working filtering past events