Search doesn't work on keys

[czottmann]

Issue description

I think the search should be applied to the keys as well. Right now it doesn't seem to be, so when I look for a particular subset of keys, I have to find them manually in the list.

Steps to reproduce the issue

1. Load any xcstrings file
2. Use search field to search for any key contained in the string catalog

What's the expected result?

The lines whose key contains the substring are shown in the filtered list.

What's the actual result?

The lines whose key contains the substring are hidden in the filtered list.

Other info

I like what you're doing here, please keep it up! :)