mobile: fix mobile interface

[rjl493456442]

This PR fixes a couple of mobile interface issues. The major one is for Interfaces.Get function.

In the previous version, the Interfaces.Get function returns a new created Interface with specifed object inside. But in the Interface.SetXXX functions, actually the object will be recreated with a difference address.

So that it means in the below code snippet, we can't change the args value through arg.

args := NewInterfaces(1);
arg := args.Get(0); 
arg.SetXXX();
// The args will not be effected at all.

[fjl]

Maybe better idea would be to make functions NewBoolInterface, NewStringInterface, etc. and use them in the template like this:

{{range $index, $item := .Normalized.Inputs}}
     args.set({{$index}}, Geth.new{{namedtype (bindtype .Type) .Type}}Interface({{.Name}}));
{{end}}

[karalabe]

I guess

args := NewInterfaces(1);
arg := args.Get(0); 
arg.SetXXX();
// The args will not be effected at all.

Is working as intended. The current way to achieve what you're trying is:

args := NewInterfaces(1);
args.Set(0, NewXXXInterface(...));

or

args := NewInterfaces(1);

arg := args.Get(0); 
arg.SetXXX();

args.Set(0, arg);

[rjl493456442]

@fjl @karalabe Update a bit since the last review. PTAL