accounting: fix layout of stats - fixes #2910

This fixes several things wrong with the layout of the stats.

Transfers which haven't started are printed in the same format as
those which have so the stats with `--progress` don't show horrible
artifacts.

Checkers and transfers now get a ": checkers" and ": transfers" label
on the end of the stats line.  Transfers will have the transfer stats
when the transfer has started instead of this.

There was a bug in the routine which shortened the file names (it
always produces strings 1 too long).  This is now fixed with a test.

The formatting string was wrong with a fixed width of 45 - this is now
replaces with the value of `--stats-file-name-length`.

This also meant that there were unecessary leading spaces in the file
names.  So the default `--stats-file-name-length` was raised to 45
from 40.

fs/config.go

@@ -110,7 +110,7 @@ func NewConfig() *ConfigInfo {
 	c.BufferSize = SizeSuffix(16 << 20)
 	c.UserAgent = "rclone/" + Version
 	c.StreamingUploadCutoff = SizeSuffix(100 * 1024)
-	c.StatsFileNameLength = 40
+	c.StatsFileNameLength = 45
 	c.AskPassword = true
 	c.TPSLimitBurst = 1
 	c.MaxTransfer = -1