deskutils/recoll: clean up the port's Makefile before next updates

• Project's web pages have been moved to their own host for clarity and security
• Undo some of the dubious whitespace changes in commit 37991a7381a0, particularly, right-shift by one tab of the entire option helpers block because X11MON_CONFIGURE_ENABLE is too long (convert to more traditional and shorter _ON/OFF knobs to avoid this in the future)
• Fix misplaced global USE_QT and make it conditional under the QT5 option as expected
• Drop no longer needed GNU_CONFIGURE_MANPREFIX, add missing hyphen in the COMMENT, etc.