Add command suggestions

[Descacharrado]

Makes suggestions when a command is misspelled as seen below.

*works in mp chats too.

Explanation:

Other commands will be recommended when a third or less of the letters (of the shortest string, either player input or actual command) are wrong. Additions, deletions, swaps and changes all count as 1 error (1 wrong letter).

• Writing 'hlep' recommends 'help' because there is only one error and the word is four letters (1/4 <= 1/3, one swap, string_utils.cpp Line 375)
• Writing 'hel' recommends 'help' because there is only one error and the word is three letters (1/3 <= 1/3, one deletion)
• Writing 'hello' does not recommend 'help' because there are two errors and the word is four letters (2/3 > 1/3, an addition and a change)
• Writing 'aawhiteboard' does not recommend 'whiteboard', even if there are only two errors out of eleven letters (2/11 <= 1/3) because the implementation is approximated and gets "lost" after two consecutive (non-swap) errors (string_utils.hpp Line 139)

The change comes from #6421 (comment) which comes from #1018

Needless to say that the implementation and thresholds are not set in stone, I even pushed all the commits so anyone can follow along the development to better understand my decisions.

[CelticMinstrel]

This looks great! I can't believe no-one has thought to do this before. I see a few small issues that need addressing, though (see specific comments below).

[Pentarctagon]

It looks like this can be merged then?