[model] Rework ability_test model

It won't be used anymore as a template for some dynamic languages
bindings, but as a standalone binary (hence the main method).
[compiler] Generate new binary test
[network] Add some output json archives
[compiler] Prepare generated code to output json
[model] Display result of get <var> call in json format
[compiler] Generate code to retrieve value of private variable

Not used in normal case (where compiler forbids it), but it is useful
for debug tool.
[compiler] Don't try to import or export opaqueType
[network] Add an overload for boost::optional<bool> in json archive

Otherwise, it returns one of null, 0, 1 instead of one of null, true,
false.
[compiler] Remove now unused code