Timestamp and reformat epoch log message

I've found it practical to know how long a given epoch has taken to train.
Also, format the losses nicer:
* Print the weighed loss, not the unweighed. This is more intuitive, and has the
  property that the stated loss is indeed the sum of its components.
* Print the loss in scientific notation, since they now can scale differently
* Use uniform distance between the fields when printing

vamb/encode.py

@@ -1,3 +1,4 @@
+import datetime
 from typing import Optional, IO, Union
 from pathlib import Path
 import vamb.vambtools as _vambtools
@@ -342,11 +343,13 @@ def calc_loss(
         kld = 0.5 * (mu.pow(2)).sum(dim=1)
         sse_weight = self.alpha / self.ntnf
         kld_weight = 1 / (self.nlatent * self.beta)
-        reconstruction_loss = ce * ce_weight + sse * sse_weight
-        kld_loss = kld * kld_weight
-        loss = (reconstruction_loss + kld_loss) * weights
+        weighed_ce = ce * ce_weight
+        weighed_sse = sse * sse_weight
+        weighed_kld = kld * kld_weight
+        reconstruction_loss = weighed_ce + weighed_sse
+        loss = (reconstruction_loss + weighed_kld) * weights
 
-        return loss.mean(), ce.mean(), sse.mean(), kld.mean()
+        return loss.mean(), weighed_ce.mean(), weighed_sse.mean(), weighed_kld.mean()
 
     def trainepoch(
         self,
@@ -393,7 +396,8 @@ def trainepoch(
 
         if logfile is not None:
             print(
-                "\tEpoch: {}\tLoss: {:.6f}\tCE: {:.7f}\tSSE: {:.6f}\tKLD: {:.4f}\tBatchsize: {}".format(
+                "\tTime: {}\tEpoch: {:>3}  Loss: {:.5e}  CE: {:.5e}  SSE: {:.5e}  KLD: {:.5e}  Batchsize: {}".format(
+                    datetime.datetime.now().strftime("%H:%M:%S"),
                     epoch + 1,
                     epoch_loss / len(data_loader),
                     epoch_celoss / len(data_loader),