Fix "install_activations" migration for sqlite.

See https://github.com/laravel/framework/issues/2694.
Fix "alter_users" migration for sqlite.

See https://github.com/laravel/framework/issues/2694.
Fix "alter_groups" migration for sqlite.

Split table actions. Ensure not null column default isn't null.

See https://github.com/laravel/framework/issues/2694.
Fix 'alter_groups_users_pivot' migration to work around sqlite issue.

Because sqlite doesn't allow for "non null" fields to have null values (logic!), the timestamps must be allowed to be null here.
Rework 'alter_throttle' migration to use drop/create for sqlite compatibility.

Since this migration effect recreates the table, it's easier to do it explicitly.
Just use 'nullableTimestamps' on all databases.
Merge branch 'sqlite-migrations' of https://github.com/joshuajabbour/sentry into joshuajabbour-sqlite-migrations
Merge branch 'refs/heads/joshuajabbour-sqlite-migrations' into develop
little migrations tweak

Signed-off-by: Suhayb El Wardany <me@suw.me>