Prusa i4 upgrades

This is a set of updates dedicated for so called 'Prusa i4' 3D printers. As I've received my printer with few broken parts (y-axis, left vertical panel broken around electricity slot) I had to design several replacement parts.
Later I made some enhancements for filament (both guide and holder) as the native was unreliable. It was made in connection to extruder locks (it lacked a power to pull a filament resulting in empty layers).
X-axis was a problem all the time, making layer shifts far too