jeffjiang: split current mixed QueryRules into three isolate QueryRules by the source of the rules

Currently, Vitess' query rules can come from three sources:

1. Tablet keyspace range from Topo Server
2. Blacklisted tables from Topo Server
3. CustomRule from local file

Mixing the three into one QueryRules structure may cause namespace confusion to users, it may also cause ambiguity when updating QueryRules. After grouping the rules by their sources, each QueryRules structure will only come from a single source, thus clarifying the namespace, which is the best for rule updating logics
Nit pick: go likes to avoid else statements. You'd rewrite this like this:
if _, ok := ...; !ok {
  return error
}
qri.querRules... = ...
...
return nil

Same comment for below use cases.