feat: allow custom output folder name

[JamesHabben]

• note: CLI and framework functionality was already in place
• GUI now has textbox to allow customization of output folder name
• guards illegal folder name characters in both CLI and GUI
• guards to prevent overwriting existing folder in CLI and GUI
• illegal character file/folder functions moved from ilapfuncs to new modularized /leapp_functions/ path
• ilapfuncs imports old functions from new path to keep backwards compatibility
• left commented out def lines in ilapfuncs to note they have been moved

[JamesHabben]