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.