[Ref] improve readability of acl code

[Ref] improve readability of acl code

Variables are used in this code for table names, making the queries hard to read.

Since there is quite a bit I've only tackled 2 patterns
1) using  where an alias within mysql would do
2) using  where an alias withing mysql would do

Ideally we want to switch to using CRM_Core_DAO::executeQuery & ditch the variables forr
table names altogether but since there is a lot I've stuck to one pattern for this change