Show/Hide delete and upload buttons according to writable status of the share

The `/shares` response JSON contains the list of shares visible to the user along with their writable status. The writable field denotes if that share is writable or not for the logged-in user. Client app must appropriately display/hide the Upload or Delete button as per the value of the writable field for a given share.

Ref: https://github.com/amahi/amahi-anywhere-specs#shares