**Warning: This commit contains a database upgrade.**
In order to add future support for retiring xpub keys, the database is
upgraded such that the keys are now stored in a dedicated bucket which
can hold multiple values rather than storing a single key as individual
values in the root bucket.
A new ID field is added to distinguish between keys. This ID is added to
every ticket record in the database in order to track which pubkey was
used for each ticket.
A new field named "Retired" has also been added to pubkeys. It is a unix
timestamp representing the moment the key was retired, or zero for the
currently active key.
Upcoming changes constitute breaking public API changes to both the
client and types modules, therefore this bumps the version numbers of
both modules and adds local replacements to go.mod files such that the
new versions can be used before they are publicly tagged.
This downgrade changes StakePoolTicketFee back to the version which does
not consider DCP-0012 activation.
This resolves an issue where Decrediton sometimes fails to pay VSP fees,
caused by Decrediton and vspd independently calculating the fee amount
using different versions of the algorithm.
Releasing the new algorithm will need to be more carefully coordinated,
potentially requiring both client and server sides to be updated in
sync.
Upgrade the dcrwallet dependency to pick up the new version of
txrules.StakePoolTicketFee which considers the status of DCP0012 in its
fee calculation.
Exporting this struct is a step towards breaking up the Start func into
a New func and Run func, enabling calling code to use:
api := webapi.New()
api.Run()
WebAPI is a more suitable name than server because it matches the
package name, and also it helps to distinguish WebAPI from the HTTP
server it uses internally (ie. webapi.server rather than server.server).
