Applications not used by items are not exported

Steps to reproduce:

1. Create a host
2. Create an application inside it, but not assign it to any item
3. Export this host
4. No info about application in the result XML

Currently, applications are being exported only as item properties:

<item type="1" key="key[blabla]" value_type="3">
<description>snmp item</description>
...
<applications>
<application>appp</application>
</applications>
</item>

Turns out, it is not possible to prepare 100500 applications without using them and export the host - all applications will be lost.