Add possibility to copy specific files/directories when parent_folder in inputs

[bastonero]

Some workflows may benefit from the possibility of restarting from just few files, e.g. when using pw.x + starting_pot='file' you may want to copy over only the charge-density.hdf5 (note here, if w/o hubbard), or when performing a nscf after a scf (this way, avoiding the use of symlinks which would modify the original folder). This is especially important if the wavefunctions are many and heavy and one does not need them.

In the suggested implementation I covered the following case scenarios:

1. The file/directory is supposed to be contained in ./out/ of parent_folder.
2. If one specifies a file in a subpath/subdir of ./out/, the subdir/subpath is created accordingly.
3. The copy of a subdir can be done via subdir/*.

The files/subdirs can be specified in the new key of settings as list of objects to copy over. The new key is restart_copy_files. The name can/should be improved.

Example:

settings = {'restart_copy_files':['aiida.save/charge-density.hdf5']}