* API change: in update signals, allow setting a start time relative
to now. This is an accuracy improvement in the case where the client
has been retrying an initial request for a while. Kind of an obscure
corner case but easy enough to address. And use a more convenient
enum representation.
* in update signals, choose `now` before acquiring the database lock.
If lock acquisition takes a long time, this more accurately reflects
the time the caller intended.
* in general, make Time and Duration (de)serializable and use them
in json types. This makes the types more self-describing, with
better debug printing on both the server side and on the client
library (in moonfire-playground). To make this work, base has to
import serde which initially seemed like poor layering to me, but
serde seems to be imported in some pretty foundational Rust crates
for this reason. I'll go with it.
I'm tired of all the boilerplate, so use the new
GPL-3.0-linking-exception license identifier instead in all the server
components.
I left the ui stuff alone because I'm just going to replace it (#111).
Add a checker for the header because it's easy to forget.
Besides being more clear about what belongs to which, this helps with
docker caching. The server and ui parts are only rebuilt when their
respective subdirectories change.
Extend this a bit further by making the webpack build not depend on
the target architecture. And adding cache dirs so parts of the server
and ui build process can be reused when layer-wide caching fails.
