Add per-group and skip cleanup options

[akhil1508]

• For tens of thousands of users on an instance, running the index command is a must before enabling the app
• Sometimes, need to re-run for a particular group so added group option
• Also cleanup itself takes a few minutes and when running per-user, it wastes a lot of time, so added skip-cleanup option that defaults to false

[akhil1508]

@pulsejet FYI, let me know if these changes are good :)

[pulsejet]

Thanks @akhil1508. BTW you can run make php-lint after make dev-setup to fix lint issues in the future.

For tens of thousands of users on an instance, running the index command is a must before enabling the app

Are you really running this with this many users? I'm curious about performance; never tested it beyond two users myself.