feat: search emails by subject/sender/recipients

[sxl613]

Client-side search to filter the message list.
Matching is case-insensitive over the sender, subject and recipients list.

I have a UAT mailcrab instance that eventually accumulates more than a 100 emails and so search would be very handy. Currently I have to scan through the list manually.

Notes:

• I tried to keep the changeset as small as possible so search is client-side only and doesn't even touch the mail content
• when searching the "Remove All" button could be misleading (since you'd have a smaller selection displayed). I figured this is acceptable
• there's no debouncing on the search

[marlonbaeten]

Thank you!