This patch updates the MinVersion and PluginVersion of all Calligra
plugins (except for Sheets function plugins and Kexi plugins) to 27 (to
reflect that current master will become 2.7). It changes the loading of
plugins from <= MinVersion to == PluginVersion since we cannot reliably
load any plugin that wasn't built against the current version.

The pigment plugins now no longer have an X-Flake-PluginVerson property,
but X-Pigment-PLuginVersion.