Homogenize config file and command line arguments of lobster-codebeamer

[phiwuu]

Only "refs" are supported by the configuration file, and as soon as #70 is merged "token" will be supported, too.
All other arguments must be specified through command line arguments and cannot be specified in the configuration file. This is a bit messy and needs to be cleaned up.

• Solution 1: Support only a configuration file
• Solution 2: Support all options through config file and command line argument
• Solution 3: Support only command line arguments (disfavored solution, because the number of configuration options is increasing and then a config file is easier to use)

In my opinion we should go for solution 1, even if it is a breaking change, for the following reasons:

• removing the support of command line arguments reduces the complexity of the code, so it is easier to maintain and test
• as said above, the number of configuration parameters is increasing, and here a config file is better for the user