fix p7zip-rar error and files with ' or " by using arg lists instead of strings

[axu2]

Not using the slightly unsafe shell=True parameter will actually throw a FileNotFoundError if I call a command that doesn't exist (like if kindlegen or 7z aren't installed). Called out explicitly here:

https://docs.python.org/3/library/subprocess.html#exceptions

So prior code in #581 actually crashed when 7z and kindlegen aren't installed during the initial check. Our code prevent selecting MOBI/zip formats afterward, so no further exceptions expected.

So added try: except blocks as needed during initial checks.

[axu2]

Also removed some utf-8 encodings since it caused crashes on files with non utf8 characters.

Now it only encodes utf8 in the same places originally.