Don't bump KDEV_ITEMREPOSITORY_VERSION in each patch version

Since b8e30215 KDEVELOP_VERSION_PATCH is greater than 255 (e.g. 220770). The way KDEV_ITEMREPOSITORY_VERSION is currently calculated assumes that KDEVELOP_VERSION_PATCH is less than or equal to 255. Otherwise, the values of KDEV_ITEMREPOSITORY_VERSION calculated for different KDevelop versions may coincide.

This commit resolves the potential issue by making KDEV_ITEMREPOSITORY_VERSION depend only on the major and the minor KDevelop versions. This has an extra benefit of clearing data repositories less often. The item repository format shouldn't change in patch versions anyway. On the unlikely occasion it does change, the responsible developer should remember to bump the KDEV_ITEMREPOSITORY_INCREMENT variable.