feat(expense-list): Display the attachment count only when the expense includes attachments

[yuvarajsai]

We can have attachments for expenses, but in expenses list we do not show if a particular expense has an attachment or not. Relates to #238

Before:

After:

Expense has attachments:

Mobile:

No attachments:

[scastiel]

This is great @yuvarajsai, thanks a lot!

I updated two things on your PR:

1. I removed the label "attachment" as we don't have translations for all languages, and I think the icon makes it pretty explicit,
2. I optimized the query to return only the document count instead of the whole document list.

[yuvarajsai]

This is my first open source PR and glad that you appreciate it @scastiel 🙌
The both changes you made make perfect sense.

Please feel free to assign any issues in this or spliit-mobile repo. I really appreciate the idea of "spliit" being an open-source project. Thank you for this initiative and your efforts.