message: Fix documentation page titles
diff: <tab type="mainpage" visible="yes" title=""/>
  <tab type="user" visible="yes" title="Tutorial" url="https://github.com/ginkgo-project/ginkgo/wiki/Tutorial:-Building-a-Poisson-Solver" />
  <tab type="user" visible="yes" title="Examples" url="@ref Examples" />
  - <tab type="user" visible="yes" title="Citing" url="@ref citing_ginkgo" />
  - <tab type="user" visible="yes" title="Contributing" url="@ref contributing_guidelines" />
  + <tab type="user" visible="yes" title="Citing Ginkgo" url="@ref citing_ginkgo" />
  + <tab type="user" visible="yes" title="Contributing To Ginkgo" url="@ref contributing_guidelines" />
  <tab type="user" visible="yes" title="Using Ginkgo" url="@ref install_ginkgo">
  <tab type="user" visible="yes" title="Installing Ginkgo" url="@ref install_ginkgo" />
  <tab type="user" visible="yes" title="Testing Ginkgo" url="@ref testing_ginkgo" />
  