Add a -do-not-transform option

[jmbau]

• Add a -do-not-transform option wich allow to not apply translation and/or rotation when converting a *.3d or *.hf file to an other file format. Usefull to center a terrain tile in Blender or to understand how to create rotors, gears, ailerons, and other moving parts.
• Fix a bug in *.obj to *.hf conversion which cause to produce a bottom/top flipped height field tga image.
• Try to automatically retrieve full texture path in *.hf to *.obj conversion.
• Fix a bug in time stamp name for files stored in ~/.local/share/v3dconverter/ during file format conversion.
• Fix some new compilation warnings. I suppose that gcc -Wall option configuration has changed...
• Update readme.txt file.
• Version number is now 0.3.3.