accounts: invalidate web user cache on changes as well

previously used app.jf.CacheExpiry = time.Now(), now either call
app.InvalidateJellyfinCache() (when we only need it to get a user),
or app.InvalidateUserCaches() (when the web user list needs to be
updated).

usercache.go

@@ -10,13 +10,24 @@ import (
 	"time"
 )
 
-// FIXME: Invalidate cache on delete/modify/etc.
-
 const (
 	USER_DEFAULT_SORT_FIELD     = "name"
 	USER_DEFAULT_SORT_ASCENDING = true
 )
 
+func (app *appContext) InvalidateUserCaches() {
+	app.InvalidateJellyfinCache()
+	app.InvalidateWebUserCache()
+}
+
+func (app *appContext) InvalidateJellyfinCache() {
+	app.jf.CacheExpiry = time.Now()
+}
+
+func (app *appContext) InvalidateWebUserCache() {
+	app.userCache.LastSync = time.Time{}
+}
+
 // UserCache caches the transport representation of users,
 // complementing the built-in cache of the mediabrowser package.
 // Synchronisation runs in the background and consumers receive