Zip multiple exported QIF files into one for all export destinations

[codinguser]

Steps to reproduce the behaviour

1. Export transactions with multiple currencies as QIF to ownCloud
2. View files at destination

Expected behaviour

3. One zip file containing all exported files

Actual behaviour

3. One QIF per currency at destination

Software specifications

• GnuCash Android version: all
• System Android version: all
• Device type: all

[rivaldi8]

Fixed in develop (c4f6a26).