Collection of API changes for v2

[ChrisSchinnerl]

This issue serves as a collection of changes we want to make to the API in the next breaking version. Whenever something comes to mind that can be improved in the current API design add it to this list.

• Update gouging settings to base unit (bytes, bytes per block etc.) instead of TiB etc.
• Merge host querying endpoints
• Merge object querying endpoints
• Remove deprecated endpoints
• Move routes that revise contracts to the bus
• Endpoint for creating multipart uploads should generate a key by default
• Forming/Renewing contracts should implicitly add them to the bus
• Remove compat code in autopilot config updating endpoint
• Don't use slab keys throughout the API but dedicated slab ids (e.g. hash of slab key)
• Remove redundant Size from content range in HeadObjectResponse
• Rename MinRecentScanFailures -> MaxConsecutiveScanFailures
• TotalCost of contracts should be InitialRenterFunds (also in db)
• Forming, Renewing and Refreshing contracts should expect maxFundingAmount > 0