index=False by default when exporting dataframes
#### Is your feature request related to a problem?

Every single time I have exported a dataframe (usually with .to_csv), I have not needed the index. 

#### Describe the solution you'd like

Change the default from True to False.

#### API breaking implications

All code that has not explicitely set index=True should make it.

#### Describe alternatives you've considered

Leave things as they are now.


Not using the index is something usual or am I biased by my own experience? 


