If the user tries to install an older version of a branded client
with shell extensions, and also install the 2.1 ownCloud client
side-by-side, both shell extensions DLLs will be registered and might
lead to both DLLs versions being loaded by exlorer, causing a system
crash.
Since we don't support both branded and non-branded shell extensions
to work at the same time, at least make sure to unregister any legacy
CLSID that could cause explorer to load the previous version DLL.
The bug seems to be in Windows when it upscales an smaller icon for
HiDPI displays. It works fine if we provide a 256x256 size in the
ico files.
Use the new square icons also used on OS X that removes the share badge
and instead has a share icon only for the OK state. This means that we
can also remove 3 icons and release 3 slots in the registry for
overlay icons (only the first few are actually loaded by explorer).
This also adds a script that uses ImageMagick to convert our SVG icons
to Windows ico files. Since ImageMagick seems to have issue doing
proper antialiasing with pixels on the edge of icons, this also
slightly scale the icons to leave 2px on each edge, out of its
logical 128px width.
