erp5_data_notebook bt5: Use dictionary to save module imports instead of saving it as list of strings.

Using dictinary its easier to update modules frequently.

For example, executing code:

'''
import numpy as np
import numpy
'''

would result as :
local_variable_dict['imports'] = {'numpy': 'numpy', 'np': 'numpy'}
which is what we expect to be saved in globals() also.