message: Update options dialog to include GUI element for reserve balance.
diff: </item>
  </layout>
  </item>
  + <item>
  + <layout class="QHBoxLayout" name="horizontalLayoutReserveBalance">
  + <item>
  + <widget class="QLabel" name="reserveBalanceLabel">
  + <property name="text">
  + <string>Reserve</string>
  + </property>
  + <property name="textFormat">
  + <enum>Qt::PlainText</enum>
  + </property>
  + <property name="buddy">
  + <cstring>reserveBalance</cstring>
  + </property>
  + </widget>
  + </item>
  + <item>
  + <widget class="BitcoinAmountField" name="reserveBalance"/>
  + </item>
  + <item>
  + <spacer name="horizontalSpacerReserveBalance">
  + <property name="orientation">
  + <enum>Qt::Horizontal</enum>
  + </property>
  + <property name="sizeHint" stdset="0">
  + <size>
  + <width>40</width>
  + <height>20</height>
  + </size>
  + </property>
  + </spacer>
  + </item>
  + </layout>
  + </item>
  <item>
  <spacer name="verticalSpacer_Main">
  <property name="orientation">
  </layout>
  </widget>
  <customwidgets>
  + <customwidget>
  + <class>BitcoinAmountField</class>
  + <extends>QSpinBox</extends>
  + <header>bitcoinamountfield.h</header>
  + </customwidget>
  <customwidget>
  <class>QValidatedLineEdit</class>
  <extends>QLineEdit</extends>
  