Check total weight at session change boundary with staking enabled

[Garandor]

Total weight of all calls at session change must be checked to ensure we're far away from the total block weight

• rotate_session
• reset_collator_performance
• staking set change
• first collator payout

Followup to #720 (comment)

[ghzlatarev]

Consider resetting collator performance over several blocks if needed. We can store the cursor in a storage item and check it in the on_initialize hook of collator_selection.
pallet_session's on_init hook gets called first and that can set the cursor, then collator_selection's on_init can continue using in the same block and in the next.

[Garandor]

Since #691 we are using the pallet_parachain_staking::Round mechanism to recompute eligible authors.
This one has a proper weight measuring mechanism instead of the full_block assumption from pallet_session.
pallet_session's session rotation hooks have since been disabled

Closing this as no longer needed.