Change tracing from qDebug() to use cutelogger, which is available under the
LGPL2.1. This allows to automatically add filename and line number to the log,
and also provides multiple log levels.

Change-Id: I5dbdaf902ba54ea99f07ae10a07467c52fdac910

Change-Id: Ibe400700f6bce0335a2975c6d635e10ae940f932

Give the user a chance to cancel the backup if the selected file already
exists. Since the filename is automatically generated from the installation
version information this can happen when trying to create a second backup of
the installation.

Change-Id: Iee34e576c4b3b94a4ccf99836741806b52a8affd

The "Installation" dialog allows backing up the current installation by
creating a zip file from the .rockbox folder since quite a while. However, this
has the drawback that you need to update your build to create a backup, but
creating a backup might be desireable in other cases as well (before updating
themes, or just for backup reasons). Since the functionality is somewhat hidden
it's also not obvious to users such a functionality exists (most users are
likely to use the "Quick Start" instead).

Implement backup functionality as dedicated dialog placed on the Uninstall tab.
Rename the Uninstall tab to accommodate this.

Change-Id: I1d2c6c8f646672d1b66bb442408fbfc2eeec700d