Update SqlWalker.php

Always be sure that only a-z characters are used for table alias, otherwise use generic "t" for "table"
rewrite tablePrefixAlias
add SqlWalkerTest for getSQLTableAlias method
#615 - assignment alignment
#615 - assignment alignment
#615 - EOF EOL fixes
#615 - Test coverage annotations
#615 - Using a data provider to build aliases for the SqlWalkerTest
#615 - sql table aliases should stay constant over time
#615 - Refactoring test case to remove duplication
#615 - Removing unused assignment
Merge branch 'hotfix/#615-enforce-A-to-Z-sql-table-aliases'

Close #615