Fix warnings on startup + saving preferences dialog

This fixes warnings on startup:
 * install xmlgui files to correct location
 * use correct indexes when adding permanent widget to status bar
 * use KActionCollection::setDefaultShortcut instead of QShortcut::setShortcut
 * use correct parser option name in main.cpp

This also fixes actions of all buttons in KomparePrefDlg where it connects to correct signals.

REVIEW: 123767