On clean remote data button and checks

[mikibonacci]

Improvements to be implemented:

• We should check only once if the CalcJobNode are empty, not eveytime we load the page/workchain. Now, for each CalcJobNode, we check the is_empty attribute. We need to verify that this is does not open ssh connections each time is it accesssed (see if it is a property). If each time it connects to remote, we should instead store an extra is_empty in the workchain, and then we only check if this attribute is not set.
• The clean button remains red even if it is disabled. We should change the color (grey).
• We should somehow also estimate the size of the remote data, so the user can decide if delete or not. See this PR in aiida-core by @GeigerJ2 : ORM: Add get_size_on_disk method to RemoteData aiidateam/aiida-core#6584

This is a follow-up of #815