[welcome] Fix up tooltips

- the "Select language" tooltip was applied to the form, so it would
   show up inappropriately all over the place
 - the buttons didn't have useful tooltips.

src/modules/welcome/WelcomePage.ui

@@ -13,9 +13,6 @@
   <property name="windowTitle">
    <string>Form</string>
   </property>
-  <property name="toolTip">
-   <string>Select language</string>
-  </property>
   <layout class="QHBoxLayout" name="horizontalLayout">
    <item>
     <layout class="QVBoxLayout" name="verticalLayout" stretch="0,0,0,0,0">
@@ -69,7 +66,7 @@
        <item>
         <widget class="QLabel" name="languageIcon">
          <property name="toolTip">
-          <string>Select language</string>
+          <string>Select application and system language</string>
          </property>
          <property name="text">
           <string/>
@@ -81,6 +78,9 @@
        </item>
        <item>
         <widget class="QComboBox" name="languageWidget">
+         <property name="toolTip">
+          <string>Select application and system language</string>
+         </property>
          <property name="sizePolicy">
           <sizepolicy hsizetype="Preferred" vsizetype="Fixed">
            <horstretch>2</horstretch>
@@ -136,6 +136,9 @@
          </item>
          <item>
           <widget class="QPushButton" name="donateButton">
+           <property name="toolTip">
+            <string>Open donations website</string>
+           </property>
            <property name="text">
             <string>&amp;Donate</string>
            </property>
@@ -146,6 +149,9 @@
          </item>
          <item>
           <widget class="QPushButton" name="supportButton">
+           <property name="toolTip">
+            <string>Open help and support website</string>
+           </property>
            <property name="text">
             <string>&amp;Support</string>
            </property>
@@ -156,6 +162,9 @@
          </item>
          <item>
           <widget class="QPushButton" name="knownIssuesButton">
+           <property name="toolTip">
+            <string>Open issues and bug-tracking website</string>
+           </property>
            <property name="text">
             <string>&amp;Known issues</string>
            </property>
@@ -166,6 +175,9 @@
          </item>
          <item>
           <widget class="QPushButton" name="releaseNotesButton">
+           <property name="toolTip">
+            <string>Open relead notes website</string>
+           </property>
            <property name="text">
             <string>&amp;Release notes</string>
            </property>