Feature request: option to --list-cache and --list-fixable

The option to list the fixed icons, or to list the caches would make this tool even more useful. Eg.:
```shell
hardcode-tray --list-cache
21-01-2019_14-17-26 [Dropbox]
21-01-2019_16-21-59 [Dropbox,Telegram]
```

A complementary option could be to list the icons, that are fixable. Eg.:
```shell
hardcode-tray --list-fixable
Dropbox
Syncthing
Telegram
```

Start at the hardcode-tray command entry point and inspect how existing command-line options expose cache and icon-fixing behavior. Define completion as --list-cache printing available cache entries and --list-fixable printing fixable icons in the formats shown in the issue; verify both options through the project's existing CLI checks.

Written by the indexing model from the issue text.