`pallet_enclave_bridge` spinout from teerex

[brenzi]

closes #187

moved stuff from teerex into a new pallet pallet_enclave_bridge and enclave_bridge_primitives

• shielding/unshielding
• confirming offchain compute
• everything concerning shards, their config and status
• encountered some brittle testing on the way....fixed it

first merge #195 !!!!!!!

[brenzi]

closing in favor of #198