Fixed check for installation of git

Forgot to revert this when testing to make sure the which command would return
1 if command not found in $PATH.
Fixed hard coded reference to .wiki extension

Switched it out for the variable. This would have broken if someone switched to
using .md (markdown) for their note syntax.
Changed lsnotes find commands

Used to use a piped combination of ls, tr, cut, sed, and grep. Now we're just
using an elegant -printf with the find command. Dear GNU folks - thank you.
Fixed find command for findnote

Was using this horrible sed expression that wasn't always reliable. Now uses find
with -printf piped to grep.
Updated git commit line for note_sys function

Says "See patch for changes" instead of diff (--patch is the git log flag
intended)

Also sent stdout to /dev/null so the user doesn't constantly see git output
every time they want to edit a note.