fixes include:
move static configuration to class declaration
use Ext.create instead of new for reload_task
use store.reload(), because store.filter() triggers no reload with
activated
remove store.guaranteeRange hack for infinite grid (works properly now)
since buffered: true is deprecated, use a BufferedStore instead
remove verticalScrollerType and invalidateScrollerOnRefresh
since this does not exist anymore in extjs6
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
