Changed some default Config-Values and Warn on specific Actions

I heared it more often that some people select their Desktops or different Directories with important Data as Output Directory....
By default my Program clears the Output dir (Including all Sub-Dirs) this is changed now, so that it can't happen so often that people lose their Data.

Changed:

• Default Config-Value "Clear output Dir before decrypt" from true to false

Added:

• A warning on changing Output-Directory while the option Clear output Dir before decrypt is turned on