Message bubbles: don't use separate column for timestamp

[maltee1]

The timestamp appears in its own column, which looks odd and wastes space, particularly in longer messages. Instead, the timestamp should be at the end of the last row, or right below it if there is not enough space. Most bubble-layout-supporting messengers do exactly that.

One might be tempted to just place the timestamp on the next row by default, but that looks odd and wastes space in short messages, particularly Single-Line messages.