Work around file manager apps not recognizing pkpass

[TheLastProject]

Some file managers seem to not correctly use application/vnd.apple.pkpass as mime type for pkpass files, making Catima not show up as option.

We should try to add a workaround for users on affected file managers.

[VasilisKos]

Confirmed on Solid Explorer.

[TheLastProject]

Interesting note: for email this seems to often be the sending client that decides the format, not the receiving client: https://github.com/thunderbird/thunderbird-android/issues/1357#issuecomment-217667602

[erAck]

Yes, the sending mail agent decides on Content-Type. In the case of application/octet-stream the receiving agent might apply some intelligence magic..