Installer: new login screen

Hi,

today I worked a bit on the look of the login screen. I know that this is normally something with minor priority but it bothered me everytime I logged into the installer. And I did that a lot the last time. ;-)

Aynway, I know that I'm not a great designer and this might not the final version but it's much nicer than the old login screen in my eyes.

Here is the changelog:

• Installer: improved the look of the login screen
• Installer: Smaller bugfixes and enhancements in error handling
• Installer: Added a "hide" button to hide the results of executed methods
• Installer: Added skeletons for gfx check methods

Greets,

Thomas