dpll.js: Fix "never ending" formula {(1,2),(-1,-2)}

Signed-off-by: Diego Giovane Pasqualin <dpasqualin@c3sl.ufpr.br>
t1.cnf was fixed, removing it from repository

Signed-off-by: Diego Giovane Pasqualin <dpasqualin@c3sl.ufpr.br>
index.html: Disable Step By Step button while solving formula

Signed-off-by: Diego Giovane Pasqualin <dpasqualin@c3sl.ufpr.br>
Update TODO