message: gui: use available space to display "Last Transaction" in peer details
diff: <item row="13" column="0">
  <widget class="QLabel" name="peerLastTxLabel">
  <property name="toolTip">
  - <string>Elapsed time since a novel transaction accepted into our mempool was received from this peer.</string>
  + <string extracomment="Tooltip text for the Last Transaction field in the peer details area.">Elapsed time since a novel transaction accepted into our mempool was received from this peer.</string>
  </property>
  <property name="text">
  - <string>Last Tx</string>
  + <string>Last Transaction</string>
  </property>
  </widget>
  </item>
  