4.7.4

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- Add support for menu monitoring.
- Allow translations of the "Xfce Panel" string.
- Add submodule to xfce4-docs/xfce4-panel-master.
- Fix accelerator key conflict (bug #6765).
- Add test for docs module and depend on xdt 4.7.3.
- Fix distributing the manual in the dist tarball.
- Translation updates (ug, gl, zh_TW, de, sk, nl, da, kk, uk, pt,
  de, it, ja, el, fi, sv, ca, eu, hu).