Change categorisation (keywords) strategy

[holzkohlengrill]

Description

This is relatively dangerous (file Emma/emma_libs/categorisation.py):

def __evalCategoryOfAnElement(nameString, categories, categoriesKeywords, keywordCategorisedElements):
    """
    Function to find the category of an element. First the categorisation will be tried with the categories file,
    and if that fails with the categoriesKeywords file. If this still fails a default value will be set for the category.
    If the element was categorised by a keyword then the element will be added to the keywordCategorisedElements list.
...
    """

Also, the *Keywords.json files should only be loaded/used when the command line flag is set.

Expected behaviour

Don't use the keywords fallback for a normal analysis an instead print a info or weak warning to std out that a category ist not in the configuration. If the categorisation file is empty skip the print to std out and display a general weak warning that categorisation is not configured.