Merge #17180: gui: Improved tooltip for send amount field

088a730 static tooltip (JeremyCrookshank)

Pull request description:

  I noticed that on Bitcoin sends the tooltip wasn't very clear for new users and I hope my PR is more concise. If it needs changing more will happily change too 👍
  ![IMG_20191017_192739](https://user-images.githubusercontent.com/46864828/67036925-75d45380-f114-11e9-88bf-bab58161f80a.jpg)

ACKs for top commit:
  laanwj:
    ACK 088a730

Tree-SHA512: 2b1103ac934d8f68d22333af3c0f5d4228b665b1e507378d4ae5b83cc2b6d6aeb46a3d68298cca93feb839db5caa560322c8df5261dc2f7db5abeed9f0dd9c69

Author: laanwj

src/qt/forms/sendcoinsentry.ui

@@ -18,7 +18,7 @@
   </property>
   <widget class="QFrame" name="SendCoins">
    <property name="toolTip">
-    <string>This is a normal payment.</string>
+    <string>The amount to send in the selected unit</string>
    </property>
    <property name="frameShape">
     <enum>QFrame::NoFrame</enum>