[win32/nsis] - don't force remove XBMC deinstallation and only migrate the
kodi userdata/portable data and show the info message to the user when
there is no Kodi folder already there (ensure that its only done at the
very first install of Kodi). Also use proper if conditions instead of
IfFileExists with offset for making it more readable.
[nsis] - move deinstallation and migration to its own helper function and
use the uninstaller for cleaning out former XBMC versions (asking the user
before) and cleaning out the former Kodi installation in the destination
directory
[win32/nsis] - use ${APP_NAME} were possible
Merge pull request #5412 from Memphiz/win32allowsbskodi

[win32/nsis/rebrand] - don't force remove former XBMC installation