Four button of navigation bar work. (#3246)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25779 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
null pointer fix

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25780 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] improve Numeric[acos((-11.4^2+5.8^2+7.2^2)/(2 5.8 7.2))] when returning degrees from inverse trig

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25781 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
web: non used GPopupMenu removed, JPopupMenu renamed for GPopupMenu

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25782 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e