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).
