Add old style mod selection in worldconfig dialog

Add error output on invalid mmdb entries

Fix RUN_IN_PLACE=0 mod install (now mods are saved in user folder in that case)
Fix text of field element not unescaped correctly

This reverts commit 39d03148.

Always use address for server
Fix first (empty) element beeing selected after deleting last world

make enter button work in create world dialog

Do a check for valid num_files before doing
assert(!m_mesh_update_thread.IsRunning());

In particular, don't execute the assertion if all media has already
been received.