Restore internal search

This request restores the internal search.

I added an option to choose between internal and external search.

I restored the local search using findutils and the search using GIO. The local search using findutils is usable because it can search binary files unlike the search using GIO. Maybe an option to use the search using GIO also for local connection should be added.

I made some fixes to the local search using findutils and added a functionality to kill the search process when canceling search.

I fixed the crashes with the search using GIO and made some other fixes.

I tested (successfully) both searches on local connections. There are problems with searching on remote connections, but remote connections don't work well (or at all), but that's a separate issue.