Bug 489922

Baloo does exclude many file types from being indexed, namely those, which are listed in

```
 ~/.config/baloofilerc
[General]
dbVersion=2
exclude filters=*~,*.part,*.o,*.la,*.lo,*.loT,*.moc,moc_*.cpp,qrc_*.cpp,ui_*.h,cmake_install.cmake,CMakeCache.txt,CTestTestfile.cmake,libtool,config.status,confdefs.h,autom4te,conftest,confstat,Makefile.am,*.gcode,.ninja_deps,.ninja_log,build.ninja,*.csproj,*.m4,*.rej,*.gmo,*.pc,*.omf,*.aux,*.tmp,*.po,*.vm*,*.nvram,*.rcore,*.swp,*.swap,lzo,litmain.sh,*.orig,.histfile.*,.xsession-errors*,*.map,*.so,*.a,*.db,*.qrc,*.ini,*.init,*.img,*.vdi,*.vbox*,vbox.log,*.qcow2,*.vmdk,*.vhd,*.vhdx,*.sql,*.sql.gz,*.ytdl,*.class,*.pyc,*.pyo,*.elc,*.qmlc,*.jsc,*.fastq,*.fq,*.gb,*.fasta,*.fna,*.gbff,*.faa,po,CVS,.svn,.git,_darcs,.bzr,.hg,CMakeFiles,CMakeTmp,CMakeTmpQmake,.moc,.obj,.pch,.uic,.npm,.yarn,.yarn-cache,__pycache__,node_modules,node_packages,nbproject,core-dumps,lost+found
exclude filters version=8
```

For many of those files it surely makes no sense to index them, however some could expect to find contents in *.h or *.cpp files. 

It would increase the UX imo if the list were exposed in the System Settings or at least a hint shown, so that a normal user knows about these exclusions and is no longer surprised or can extend the list on their own.