Export commands should accept output file as parameter

[edno]

Export commands should accept an optional parameter for customised export filename and path.

• [x] php artisan export:accounts
• [x] php artisan export:categories
• [x] php artisan export:groups
• [x] php artisan export:whitelist

[edno]

Also supported by command export.

If file exists at target location, then confirmation is requested.

$ php artisan export /tmp 
 1/1 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%

 Overwrite existing '/tmp/accounts/accounts.txt' ? (yes/no) [no]:
 > 

Using --cli overwrites target location by default.

[edno]

Tests to be implemented before closing this ticket