move ImplWindowAutoMnemonic into DoInitialLayout

so Floating windows get automnemonics as well, e.g.
the Floating Sort floating window of reportdesign

Change-Id: I0805840f7b0b2329e210c77e32c5eabfdac387fb
convert RID_GROUPS_SORTING floating window to .ui

(recovers icons for up/down/delete in the process)

Change-Id: I85a8de2ebe1321f972000a680a9f4308c26ae4c3