Fix antiscia/aspect change buttons

The javascript code ran by Astrognome is changing the visibility
attribute instead of style attribute, but style has precedence.
Disable chart context menu

Commit 2af46ec accidentally re-added chart context menu by removing the
context-menu signal handler from the web view. This patch disables it again.
Merge pull request #66 from gergelypolonkai/fix-context-menu

Disable chart context menu
Merge branch 'master' into city-chooser