Add support for Sia alerts

[tbenz9]

/daemon/alerts is a new API endpoint that is meant to tell users what is wrong with any modules they are running. It would be awesome to display those alerts somewhere.

https://gitlab.com/NebulousLabs/Sia/merge_requests/3769

[n8maninger]

The new alerts in Sia will definitely be displayed right alongside the current alerts in Host Manager once its more finalized and ready on the Sia side.

[n8maninger]

Removing the milestone, Sia's built in alerts only support one host alert at the moment and Host Manager already has a similar alert. At this point Host Manager's alerts are much more robust. Will look at again at a later date.

Sia's Alerts:

• HostInsufficientCollateral

Host Manager Alerts:

• ContractsNotAccepted
• NotEnoughCollateral
• IncorrectConsensus
• FailedContracts
• IncorrectContractStatus
• ConnectionError
• StorageFolderFailedReads
• StorageFolderFailedWrites
• StorageFull
• StorageAlmostFull
• StorageNearFull
• StorageUnder4TB
• NoStorageAvailable
• WalletLocked
• WalletRescanning
• WalletEmpty