Use toLatin1() instead of toAscii() for Qt5-compat

Since we don't call QTextCodec::setCodecForCStrings()
QString/QByteArrays::toAscii() is the same as toLatin1() according to
the Qt4 documentation.

In Qt5 toAscii() got removed completely.
XML files (backupStarted.xml backupEnded.xml and scheduler.xml) for backup surveillance are written to the server
Cleaning up BackupThread object after use to prevent possible memory leaks
Added client identification to the XML which will be uploaded to the server
backupID has is now from datatype long, using QTemporaryFile for local scheduler.xml, backupStarted.xml and backupEnded.xml
Modifications after reviewing the code with dev-zero
About dialog redesigned

* Removed images from copyright and development company
* Put 'Copyright by' and 'Developed by' on the same line
* Use Sepiola logo if no reseller is set
Removed unused include
Default application shows name and version on the lefthand side of the logo
About dialog redesigned