Add tooltips for accessibility

Most of the UI was lacking tooltips for accessibility.
This patch is a roundup of all the fields, buttons, and selectors,
for setting up a first stone to build upon.

Change-Id: I63f5e9aa1c5e96c61fd04540df50895579bb293d
Reviewed-by: Anthony Léonard <anthony.leonard@savoirfairelinux.com>
diff --git a/aboutdialog.ui b/aboutdialog.ui
index 56be482..50f6277 100644
--- a/aboutdialog.ui
+++ b/aboutdialog.ui
@@ -458,6 +458,9 @@
      </item>
      <item>
       <widget class="QPushButton" name="aboutButton">
+       <property name="toolTip">
+        <string>about button</string>
+       </property>
        <property name="text">
         <string>About</string>
        </property>
@@ -471,6 +474,9 @@
      </item>
      <item>
       <widget class="QPushButton" name="creditsButton">
+       <property name="toolTip">
+        <string>credits button</string>
+       </property>
        <property name="text">
         <string>Credits</string>
        </property>