Smart re-compilation

[finger563]

Don't recompile (even if the user asks) unless the model or code have changed. If not all architectures have binaries, or if the software model has changed, only then start recompilation process. Otherwise simply use previously created binaries.

[finger563]

Should be able to use commit hash stored in meta-data.json and compare to current commit hash at least.

[finger563]

Doing smart re-compilation is a little too hard at the moment, since it requires keeping track of attribute changes to code-related objects. Could possibly be handled by an add-on in the future that interacts with an executor.