We can now step into library code in the debugger.
Since we now need the whole source code of our libraries
(and not just the headers), we clone the whole serenity git repo into
/usr/share/serenity.
This patch adds a context menu to variables in the debugger variable
tree view that has an option to set the value of a variable. An input
box will pop up asking for the new value of the variable, which
is then parsed and used to set the actual variable.
