Added wrapper for the Melkor mutator

Added a wrapper for the IO Active's Melkor ELF mutator. It requires the following patch:

https://github.com/joxeankoret/Melkor_ELF_Fuzzer/commit/d1fb577b5202e1763b743da143f8e5b45cf962c6

In order to add the 2 new mutators the following SQL commands must be executed:

 * insert into mutation_engines (name, description, command, date) values ('Melkor mutator', 'Melkor is a very intuitive and easy-to-use ELF file format fuzzer to find functional and security bugs in ELF parsers.' , '%NIGHTMARE_PATH%/mutators/melkor_mutator.py %TEMPLATES_PATH%/%FOLDER% 10 %OUTPUT%', current_date);

 * insert into mutation_engines (name, description, command, date) values ('Melkor mutator multiple', 'This is a wrapper using Melkor mutator to create a zip file with multiple fuzzed samples inside. Useful to fuzz Antivirus engines.', '%NIGHTMARE_PATH%/mutators/melkor_mutator_multiple.py %TEMPLATES_PATH%/%FOLDER% 20 %OUTPUT%', current_date);