[PDI-12565] LIKE pattern matching of meta

1. When querying tables and columns in Thin JDBC meta, use SQL-LIKE pattern matching.
 * '_' wildcards a single character.
 * '%' wildcards any number of characters.
 * Pattern is converted to a regular expression. All regex characters in pattern are escaped before matching.

2. getString should always returns String
 * if value is set, casting value to string
 * null is returned if column value is not set

http://jira.pentaho.com/browse/PDI-12565