verdi code list should hide codes on unconfigured computers

[ltalirz]

Currently, when importing codes & computers from AiiDA export files, the imported computers are hidden in verdi computer list but the imported codes are not hidden in verdi code list.

I suggest codes on computers that are not configured should be hidden by default (fine to show them with --all).

P.S. When importing a computer with a name that already exists in the database, the following suffix is appended:

aiida-core/aiida/tools/importexport/common/config.py

Line 24 in f70d09f

DUPL_SUFFIX = ' (Imported #{})'

This is not very user friendly, since it leads to computer names like fidis (IMPORTED #0) that force users to use quotation marks.

I propose to change this to fidis_IMPORTED_#0 or some user-friendly alternative.

@CasperWA Sounds reasonable?