[FIND] Rewrite of the find utility. (#1553)

[FIND] Rewrite of the find utility. (#1553)

This commit contains a complete rewrite of find console utility.
The goal of it was to make the source code easier to maintain
and to add a missing feature (/offline switch).

Additional changes:
 * now the program operates on Unicode strings;
 * added conutils and shlwapi as program's libraries;
 * added IDS_INVALID_SWITCH string into resources;
 * modified IDS_USAGE string to include /offline switch
   description.

https://ss64.com/nt/find.html was used for reference.