GUI: rename Pot reset button to "Set" and move it next to its spinbox

Now that doubleSpinBox_pot_temp carries the target temperature, the
old "Pot reset to ambient temperature" label no longer described what
the button does and reserved far more width than a short label needs.
Shortened to "Set" and repositioned immediately to the right of the
Pot [°C] label/spinbox it applies, with both shifted left to fill the
space the long label used to need.

client/brewpi.ui

@@ -3742,9 +3742,9 @@
    <widget class="QPushButton" name="btn_pot_reset">
     <property name="geometry">
      <rect>
-      <x>700</x>
+      <x>880</x>
       <y>500</y>
-      <width>220</width>
+      <width>70</width>
       <height>31</height>
      </rect>
     </property>
@@ -3752,13 +3752,13 @@
      <string>Only available when the server's Pot is simulated</string>
     </property>
     <property name="text">
-     <string>Pot reset to ambient temperature</string>
+     <string>Set</string>
     </property>
    </widget>
    <widget class="QLabel" name="label_pot_temp">
     <property name="geometry">
      <rect>
-      <x>930</x>
+      <x>700</x>
       <y>500</y>
       <width>91</width>
       <height>31</height>
@@ -3774,7 +3774,7 @@
    <widget class="QDoubleSpinBox" name="doubleSpinBox_pot_temp">
     <property name="geometry">
      <rect>
-      <x>1030</x>
+      <x>800</x>
       <y>500</y>
       <width>70</width>
       <height>31</height>