SettingsAccessor: Add QWidget *parent parameter to saveSettings

The PersistentSettings::writeFile needs it, and SettingsAccessor
should not hardcode it to Core::ICore::mainWindow()

Change-Id: I6ca99e9cd861fd81337028055fe0ed4d158b152f
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Quieten warning about unused parameter

Change-Id: I78976e34a0b98e851c7852116a588b0f49009267
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
SettingsAccessor: make FileAccessor::assignSuffix a static function

Also make sure the sanitization of the suffix happens for both
possible suffixes and not just for the first one.

Change-Id: I5d34582323ce147bdf4638e5ec3321227d329609
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
UserFileAccessor: Assume that qtversions/toolchains files can be read

We do not want to produce output here when those files can not be found,
that is a perfectly normal thing nowadays. So do not produce any output.

Simplify the code a bit now that we do not need to do extra checking.

Change-Id: Ifdfe3148e8a350bf3cd2aca5e78c2458274d75f9
Reviewed-by: Daniel Teske <daniel.teske@digia.com>