Implemented ticket #210 "Add procedures to the autocompletion"
Changed font of procedure icon
Provided icon for procedure autocompletion
Implemented ticket #199 "Implement NaNs in zeroes and extrema"
Implemented ticket #198 "Improve error messages" - Added some information to a few error messages - Further changes will be done on-the-fly
Implemented part of ticket #198 "Improve error messages" -> Changed the internal error management
Fixed issue #209 "Logical operators in strings are interpreted"
Fixed issue #208 "Files only containing comments cannot be read"
Implemented ticket #207 "Focus terminal, if shown by pressing "F2""
Implemented ticket #206 "Implement "fold current block" functionality"