#8 KnowME:Multimedia filelist not refreshed if new kb is loaded

[akrawczyk]

Steps to reproduce:
- open a kb with integrated multimedia files
- click on "Multimedia"
-> files are listed

- now load another kb with no multimedia files in it
- click on "Multimedia"

Expected:
the list is empty

Actual:
the files from the last opened kb are listed.

If the new kb is saved, the multimedia files are included.