Port twain plug-in to the new plugin framework

This requires MR !298 (merged) to build the plug-in using meson or manually enable it by editing /plug-ins/common/meson.build.

Since this is the first time I ported a plug-in I thought it better to use a MR. I also already started it before getting direct access.

Note this only works on 32 bit Windows the same as the old plug-in. Tested myself with a Canon scanner and works for me.