uim: fix packaging issues

* I'm not sure if these belong to uim-xim or rather uim-gtk2.0/uim-gtk3
  but original author obviously doesn't care so I'll follow the
  uim-candwin-gtk example and put them all in uim-xim
* fixes:
  uim-1.8.6: uim: Files/directories were installed but not shipped in any package:
  /usr/libexec/uim-candwin-horizontal-gtk
  /usr/libexec/uim-candwin-gtk3
  /usr/libexec/uim-candwin-tbl-gtk3
  /usr/libexec/uim-candwin-tbl-gtk
  /usr/libexec/uim-candwin-horizontal-gtk3
  Please set FILES such that these items are packaged. Alternatively if they are unneeded, avoid installing them or delete them within do_install.
  uim: 5 installed and not shipped files. [installed-vs-shipped]

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>