update: separated plug from gaugedUniERC20

[shreykeny]

Changes

• Created MultiGaugeUniERC20, ConnectionPlug & MultiGauge

MultiGaugeUniERC20

• Removed PlugBase from MultiGaugeUniERC20
• uniTransfer : Instead of calling Socket outbound directly, MultiGaugeERC20 calls a specific ConnectionPlug contract which is connected to a specific switchboard.
• uniReceive called by respective ConnectionPlug to mint tokens instead of Socket directly

ConnectionPlug

• Each MultiGaugeUniERC20 will have multiple ConnectionPlug, each configured to desired switchboard
• MultiGaugeUniERC20 calls connection plug to send burn message to destinationChain via configured outboundSwitchboard
• ConnectionPlug calls receiveInbound to mint tokens on destinationChain via configured inboundSwitchboard

MultiGauge

• Changed mapping from mapping(uint32 => Limits) public bridgeLimits to mapping(address => Limits) public bridgeLimits
• Changed _siblingChainSlug to _bridgeType for all methods