Check required lang runtimes when running wws (from .wws.toml)

[Angelmmiguel]

As part of the wws initialization, it will retrieve the data from the .wws.toml file (#67). Then, it will use the runtime manager (#66) to check if the required runtimes are installed. If they are missing, it will install them by default in the current folder.

This step is required as runtimes may add more supported extensions to wws. For example, by default wws cannot support workers written in Python. However, they may add a Python runtime and wws will start managing .py files as workers.

If this step fails for any reason, wws will show a warning and will continue with the remaining supported extensions.