[utils] Add a function to reload all modules

[5iver]

Is your feature request related to a problem? Please describe.
Reloading modules can be tricky, and it can be confusing for new users of the libraries. Modules need to be reloaded when testing changes to them.

Describe the solution you'd like
Add core.utils.reload_modules, which will reload all modules.

[mjcumming]

Great idea. If the core reloads does that mean all personal modules reload?

[5iver]

I haven't dug into this, but I think it will be possible to reload all modules. I'll remove the reference to 'core modules'.