Do not double reload
Restore history selection on relaod

https://bugzilla.gnome.org/show_bug.cgi?id=702686
Remove dark grey from the palette

gitg uses a palette of colors for drawing the
history graph of a repository. One of the colors
of the current has very insufficient contrast when
using a dark GTK theme.

https://bugzilla.gnome.org/show_bug.cgi?id=710127