Check for unwanted extensions in the NZB

[Safihre]

Supported by: https://forums.sabnzbd.org/viewtopic.php?f=3&t=24804

We only check inside the rar-files if there are unwanted extensions.. but what if they are just as a file inside the main NZB? We should detect those to.

[sanderjo]

WIP: Detection is working, and failing works too, but in an ugly way ...

EDIT: Oh, wait, this post is very special: one very big EXE, plus par2 files. So when my prototype threw away the EXE, ... the download failed completely correctly. Let met check with a download with rar and par2 files, plus some "handy"codec.exe ...

[sanderjo]

With the same code, and a fabricated with EXE in plain sight, and the rest just in plain RARs (NZB here: https://raw.githubusercontent.com/sanderjo/NZBs/master/reftestnzb_small_post_with_EXE_as_plain_file.nzb ), the code works quite nicely:

• On NZB import, the EXE file is skipped, with a warning.
• The rest is imported, and succesfully downloaded.

@Safihre I just skip the EXE (and other unwanted extensions). No pausing. I see that as the only feasible to do, without too much code overhauling.